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COUNTERFEIT DETERRENT FEATURES FOR THE NEXT-GENERATION CURRENCY DESIGN
4
DESCRIPTION AND ASSESSMENT OF DETERRENT FEATURES
A number of features are now being used in U.S. currency to deter counterfeiting, and many additional ones are being considered for future use to respond to the projected threats. This chapter contains a description of and results from the committee's assessment of categories of counterfeit-deterrence features that represent a wide variety of technologies. In line with the objectives of this study, the emphasis is on those features that are visible to the unaided eye. But less obvious features that can be easily inspected using relatively inexpensive aids have also been included. The first section discusses the features that are currently incorporated in U.S. banknotes. The following section discusses candidate features, grouped by generic classes. The last section is a summary of the recommendations.
Discussion of two types of visible deterrent features is contained within this chapter: passive and active. A passive feature is one that is difficult to reproduce or simulate in its own right; if it is copied or simulated, the fake can be detected by examining the quality of the reproduction. An active feature may not be an obvious feature on a genuine note; however it interacts with the reprographic process in some way, resulting in an obvious indication on the duplication attempt. The security thread is an example of a passive feature; an aliasing pattern is an example of an active feature.
Within the discussion of each feature class is a description of the feature, its significant advantages and limitations, and the committee 's assessment. The committee was guided by evaluation framework (presented in the previous chapter) in performing the assessment.
In some instances, a strong synergistic deterrent effect was found between features that were placed in different classes. Each class was assessed separately, but where appropriate the discussion points out the possible increase in effectiveness if one feature is used in conjunction with another. For instance, color by itself was not assessed to be a particularly effective deterrent; but the effectiveness of moiré patterns can be enhanced through the appropriate use of color. Suggested criteria for integrating multiple features are further discussed in the next chapter.
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COUNTERFEIT DETERRENT FEATURES FOR THE NEXT-GENERATION CURRENCY DESIGN
4
DESCRIPTION AND ASSESSMENT OF DETERRENT FEATURES
A number of features are now being used in U.S. currency to deter counterfeiting, and many additional ones are being considered for future use to respond to the projected threats. This chapter contains a description of and results from the committee's assessment of categories of counterfeit-deterrence features that represent a wide variety of technologies. In line with the objectives of this study, the emphasis is on those features that are visible to the unaided eye. But less obvious features that can be easily inspected using relatively inexpensive aids have also been included. The first section discusses the features that are currently incorporated in U.S. banknotes. The following section discusses candidate features, grouped by generic classes. The last section is a summary of the recommendations.
Discussion of two types of visible deterrent features is contained within this chapter: passive and active. A passive feature is one that is difficult to reproduce or simulate in its own right; if it is copied or simulated, the fake can be detected by examining the quality of the reproduction. An active feature may not be an obvious feature on a genuine note; however it interacts with the reprographic process in some way, resulting in an obvious indication on the duplication attempt. The security thread is an example of a passive feature; an aliasing pattern is an example of an active feature.
Within the discussion of each feature class is a description of the feature, its significant advantages and limitations, and the committee 's assessment. The committee was guided by evaluation framework (presented in the previous chapter) in performing the assessment.
In some instances, a strong synergistic deterrent effect was found between features that were placed in different classes. Each class was assessed separately, but where appropriate the discussion points out the possible increase in effectiveness if one feature is used in conjunction with another. For instance, color by itself was not assessed to be a particularly effective deterrent; but the effectiveness of moiré patterns can be enhanced through the appropriate use of color. Suggested criteria for integrating multiple features are further discussed in the next chapter.
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CURRENTLY USED OVERT U.S. COUNTERFEIT-DETERRENCE FEATURES
U.S. currency presently in circulation has a number of features that serve to deter counterfeiting. Some of the features can be authenticated at points of sale through unaided visual inspection by inspection using a low-power magnifier or similar simple device. Other features require relatively sophisticated instrumental aids and will not be discussed further. This report focuses on overt, visible features that serve as counterfeit deterrents.
Paper
U.S. currency is printed on a special paper composed of cotton and linen fibers with no wood fibers or starch. Stringent specifications describe the fiber configuration, thickness, weight, color, and reflectance to ensure uniformity and durability of the paper (BEP, 1991). It has a distinctive feel that is readily detectable by many people who handle large amounts of currency; they can easily identify counterfeits that are not printed on the appropriate paper. Many of the counterfeits are detected at points of transaction by having a wrong “feel.” This distinctive paper, in combination with intaglio printing, provides significant counterfeit deterrence at a moderate cost. The BEP requires strict control of currency paper to ensure that it is not available to potential counterfeiters. Unauthorized possession or control of this or similar paper is a criminal offense. While it is theoretically possible that counterfeiters could make paper that is identical to the U.S. currency paper, it would be a major effort, requiring significant technical expertise, equipment, and monetary resources.
Red and Blue Fibers
U.S. currency paper contains red and blue fibers that are added to the paper slurry and become randomly dispersed throughout the paper. These fibers are observable visually; however, it requires close inspection in good lighting to detect them. The fibers represent a deterrent to the professional counterfeiter who must add two colors to his palette for a high-quality forgery. However, the red and blue fibers can be simulated by drawing red and blue lines with a pen or pencil or, possibly, by printing them. Such simulations would most likely pass casual visual inspection but not careful inspection with a magnifier. The casual counterfeiter will most likely find the color copy reproduction of the fiber quite adequate. The red and blue fibers do not provide a high level of counterfeit deterrence for detection at points of sale, but they are relatively inexpensive. They could also be enhanced, as discussed in a later section.
Intaglio Printing and Fine-Line Engraving
The intricate designs used in existing U.S. banknotes represent a significant deterrent feature that is already in place. The variations in the fineness and depth of the line work,
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which are produced by master engravers, give an intaglio-printed note its characteristic embossed or raised “feel” (Buckley, 1992). The variation of line width in a portrait or a sculptured border gives an appearance of gray-level and depth to the imagery that is very difficult to reproduce—most counterfeit notes simply do not look “right.”
Intaglio is a complex printing process commonly used for printing high-security documents. The process starts with the fabrication of master printing plates containing the fine-line engraving, incised by hand by skilled engravers. The master plates are used to produce the production plates that are used in the printing presses. Intaglio printing presses require a specially formulated high-viscosity ink that is applied to the grooves in the plate. The plate is wiped to remove all of the ink except what is captured in the grooves. The plate is then pressed against the paper under a very high pressure (typically 7,500 to 15,000 psi) to transfer the ink and emboss the paper (Graminski, 1993a). The plates are wiped clean after each impression. (Generally, approximately 15 percent of the ink actually is transferred to the banknote. Graminski, 1993b). The remainder is removed during the wiping operations.)
The embossing effect and the thick layer of printed ink causes the printed lines to be raised, giving the notes a distinctive look and feel. This produces lifelike portraits that cannot be exactly duplicated in counterfeits made by other printing processes or by copiers and printers. Similarly, the complex, unbroken fine-line patterns in the borders of the notes and in the backgrounds of the portraits are not duplicated well by lower-resolution copiers or printers.
The intaglio printing process is used for the black print on the front side of the notes and the green print on the back side. The Treasury seal, Federal Reserve seal, and serial numbers are printed by a typographic or letterpress process. In a letterpress, the characters to be printed are formed by raised surfaces on the printing dies. A roller applies ink to these raised surfaces and then the die is pressed against the paper to transfer the ink.
Microscopic inspection reveals unique characteristics of intaglio and letterpress print that distinguish them from other types of print. For example, the high pressure applied to the ink when the printing plates are pressed against the paper during intaglio printing forces ink into the spaces between the paper fibers, beyond the edges of printed lines. In letterpress printing, the pressure between the plate and the paper tends to squeeze ink to the edges of the raised characters, leaving an obviously thicker layer of ink along the boundaries.
Figures 4-1 through Figures 4-3 contain a series of photomicrographs, taken at 11-power magnification, of the eye in the engraved portrait of Alexander Hamilton on a $10 banknote. Figures 4-1 is the image as printed by the BEP using the intaglio process. The distinctness of the lines and the bleeding of ink (or “feathering ”) along the fibers is evident. Figures 4-2 is a photomicrograph of the same area that has been photocopied. Note the loss of detail and the inability of the process to reproduce the sharp lines. The toner particles are clearly evident.
Figures 4-3 is a photomicrograph of the same area again, this time from a counterfeit note produced using the lithographic process. Again, the image is clearly different from the intaglio one. The raised border and loss of definition can be seen. The amount of detail is greater than that of the photocopies note, but less than that of the intaglio printed note. In addition, the tactile feel of U.S. currency is extremely difficult to exactly reproduce using other printing or duplication methods. The committee judges intaglio printing of fine-line engravings to be an effective deterrent, particularly if a low-power magnifier is used as an aide for detection.
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FIGURE 4-1 Photomicrograph of intaglio printed image.
FIGURE 4-2 Photomicrograph of photocopied image.
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Figure 4-3 Photomicrograph of lithographic printed image.
However, the intaglio printing equipment employed by the BEP has several limitations that prevent some potential deterrent features from being incorporated. For instance, those counterfeit-deterrence features that depend on accurate registration of printed features between the front and back sides of the note would not be possible to produce on the existing intaglio equipment, even assuming ideal conditions. The BEP prints currency in 32-note sheets. The green print forming the backs of the notes is printed first and allowed to dry. Then the black print for the front side is applied. The very high pressure produced by the printing plates tends to stretch the paper. This causes errors in registration between the front and back images, even if the sheets have been placed into the press very accurately. Exact registration would require simultaneous, or near simultaneous, printing of the front and back images.
As another example, the current BEP intaglio equipment is limited in its ability to print additional colors. Multiple colors can be printed by selective inking of the printing plates. However, only a restricted number of fountains are available in which to hold additional ink colors.
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Serial Numbers
There are two serial numbers printed in the same green ink as the Treasury seal on the face of each note. No two notes of the same series, bank, and denomination have the same serial number. The Federal Reserve banks are designated by a letter and a corresponding numeral. The first character of the serial number is a letter that designates the Federal Reserve Bank and matches the letter in the Federal reserve seal. The corresponding numerical designation of the Federal Reserve Bank is printed in four locations on the face of each note.
The serial numbers and Federal Reserve Bank designators are faithfully copied on counterfeits made by copiers or electronic printers. A large number of copies of the same note, with the same serial number and bank designators, is subject to detection by alert point-of-sale or bank personnel. The serial numbers and bank designators are a more effective deterrent to the printing of notes on printing presses. The relationship among the features is not commonly known, although it is public information. Even professional counterfeiters are not aware of the simple relationship. But neither are personnel at points of transaction. Therefore, it is not normally used as a means of counterfeit detection. Making notes with different serial numbers complicates the printing process for the forger.
The denomination of each note is printed in intaglio in each corner on both sides of the notes and is spelled out in the lower border. It is also printed in black ink where it is overprinted with the green Treasury seal. The large number of denomination indicators is a deterrent to attempts to upgrade notes by simply altering the denomination numbers in the corners of the notes. Also, a distinctive portrait on the front of the note is associated with a particular denomination, as is a distinctive back. (This was one of the important changes made during the last major currency-redesign effort, which occurred in 1929.)
Security Thread
The BEP began incorporating a security thread in the Series 1990 banknotes. It was first introduced in the $100 notes and then subsequently in the $50, $20, and $10 notes. This thread is a thin metallized polyester strip 1.4 to 1.8 mm in width, and 10 to 15 µm in thickness (BEP, 1990). It is placed in the paper during its manufacture. It is located in the clear field between the border of the note and the Federal Reserve seal. The letters “USA” and the denomination of the note are printed on the thread. The thread is contained within the paper substrate so that it is not observable in reflected light and cannot be reproduced by the reflected light of copiers. The thread and its printing can be detected visually in transmitted light. A deliberate action (holding the note up to the light) is required for visual detection of the existence of the thread and especially to read the printing on it. It is the committee's opinion that at the present time, the public is not generally aware of this security feature or how to authenticate it. Therefore the security thread 's deterrence potential has not yet been fully exploited.
The thread can be simulated to pass casual inspection by drawing, printing a white line with an opaque white ink, or pasting on a thin sheet of paper. It would be easy to simulate the printing on the thread using the latter approach. If the simulation was done first, followed by the banknote printing, the simulated thread would be more difficult to detect as a forgery.
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Even though the security thread was not originally developed to be easily machine detectable, readers are available that can detect the existence and the location of a metallized thread; these readers can be fooled if the counterfeits contain a metal strip or wire in the appropriate location.
The security thread has been incorporated into 45 percent of the $100 and $50 notes in circulation worldwide; status for lower denominations are not available. It will be incorporated into $5 notes in 1994. When most of the notes in circulation have the security thread (estimated to be 1995) and the public is educated better about its existence and how to authenticate it, the security thread will be a reasonably effective counterfeit deterrent.
Microprinting
Concurrent with the introduction of the security thread in the Series 1990 banknotes, the words “THE UNITED STATES OF AMERICA” have been printed repeatedly around the portrait in a very fine line, 6 to 7 thousands of an inch wide. The print appears as a thin line to the naked eye, but the lettering can easily be read using a low-power magnifier. The resolution of most current copiers is not sufficient to copy this fine print, but equipment beginning to appear in the marketplace has sufficient resolution to copy it. The microprint is at the limit of resolution of the intaglio printing process; therefore, it will not be possible to use intaglio microprint to deter reproduction by higher-resolution copiers and printers.
Color
The light-green tint of authentic currency paper is difficult to reproduce and is one feature distinguishing this paper from commonly available paper. Since currency paper contains none of the fluorescent whiteners that are common in commercial papers, it will not fluoresce under an ultraviolet light. This provides a simple means of detecting suspicious notes, but is not a foolproof method. For example, genuine notes that have been washed might exhibit fluorescence due to whiteners present in laundry detergents.
Overall Assessment of Existing Visible Features
The existing counterfeit-deterrence features cannot be authenticated easily and unobtrusively by inexperienced and untrained personnel at points of sale.
Detecting the unique feel of authentic currency paper requires experience in handling currency. But the feel of the paper changes with wear.
The distinctness of intaglio printed images can be observed with a low-power magnifier, but this requires experience (and time) to do. And, the richness of the intaglio images becomes harder to discern as the banknotes wear in circulation.
The simple relationship between the serial numbers and the Federal Reserve Bank indicators is not known by most cashiers. It does require a certain amount of concentration.
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Most people do not pay particular attention to serial numbers and will rarely notice multiple bills with the same serial number.
The red and blue fibers can be detected only with a very close inspection in good lighting.
Reading the microprinting requires the use of a magnifier; but the advanced copiers and printers that are becoming widely available will be able to satisfactorily reproduce it.
The polyester strip can be detected only by holding the note so it can be observed in transmitted light.
In summary intaglio printed fine-line engravings on a yellow-green tinted paper has been very effective in the past in allowing the general public to readily identify notes that “aren't right.” However, with the availability of high-quality color copiers and printers, these deterrents will become much less effective over time. As has happened before in history, the existing overt counterfeit-deterrence features of U.S. currency require upgrading to respond to new counterfeiting threats that are driven by advanced technology.
INNOVATIVE VISIBLE COUNTERFEIT-DETERRENCE FEATURES
A number of innovative counterfeit-deterrence features have been proposed for incorporation into U.S. currency. These features can be categorized as substrate-based, printed, multicolored, design-based, post-printed optically variable, and random pattern with encryption and as deterrents built into copiers and printers.
Substrate-Based Features
The use of a particular, high-quality paper substrate represents the first line of defense of U.S. currency. As currently produced for Series 1990 bills, the paper stock incorporates a number of security features, including a denominated metallized polyester security thread, red and blue fibers, and a distinctive tint. The physical properties, fiber composition, and surface treatment are closely specified and subjected to careful quality control. Substrate-based deterrent features cannot be exactly reproduced and are therefore particularly attractive deterrent features. A large number of additional substrate-based features have been suggested, and several of these are currently employed in foreign currencies. An assessment of the generic types of substrate-based features follows.
Laminated Substrates
The ability to produce currency paper by joining two half-thickness sheets with or without a very thin plastic interleaf provides many possibilities for the introduction of deterrent features to the substrate (James River, 1993). For example, designs, images, or text can be printed on what becomes the interior of the note. Such printed information would not be visible in reflected light but would be apparent on viewing in transmitted light. If a plastic interleaf is employed, transparencies could be introduced. In effect, then, the current features
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of the security thread could be extended over the entire note. The sophisticated paper-making technology that is available to produce and join the half-thickness sheets makes this a potentially attractive deterrent.
The committee views the laminated substrate as a system capable of incorporating multiple security features. These systems in paper/paper, paper/plastic and plastic/plastic laminates have undergone substantial development and are in use for some security document applications (paper/paper) and, in one case for currency (plastic/plastic in Australia). The promise of this technology recommends a careful monitoring of the progress in their development and experience in various applications. The ability of the adhesive that joins the laminates to withstand intentional separation of the layers is a particular area of interest.
Skilled counterfeiters could probably readily simulate these laminates, as well as any of the features contained within the laminate. They would not be concerned with durability of the note, making the task much easier than that of the genuine paper maker. Paper splitting and re-bonding with glue is one possible simulation route; another would involve bonding two thin sheets of paper.
Plastic Substrates
As mentioned above, plastic can be substituted for paper as the substrate material, as has been done in Australia for its $10 note. Plastic provides a smoother surface for microprinting, and hence finer details can be printed. It also makes it relatively easy to introduce transparencies. The plastic may itself incorporate various additives and deterrent features. Some increase in substrate durability may be anticipated but there may be problems with heavy creasing in the bills leading to premature cracking (Haslop, 1993a).
There are a number of problems with using plastic substrates for a note. First, the feel of a plastic note would be substantially different from that of a paper note. It may be more difficult to develop a distinctive feel for a genuine plastic banknote, as has been done for the current paper ones. And thin plastic material is readily available and would be impossible to restrict. Also, plastic is currently more expensive than paper. Many of the security features associated with paper substrate (e.g., watermarks) are not possible with a fully plastic substrate. But similar features are possible; for example, a shadow image can be produced in the plastic coating that can have the same functionality as a watermark. it's also sensitive to the ink composition and printing parameters regarding durability issues such as ink adherence, temperature, and humidity effects.
Most of the benefits associated with a plastic substrate can be achieved with laminated paper structures, or innovative extensions to the current substrate material. All of the U.S. experience and testing procedures are based on the current substrate material. At this time, there does not appear to be a significant enough advantage to plastic substrates to overcome the cost of conversion.
Enhanced Security Thread
A security thread has been introduced in Series 1990 currency in denominations of $10 and higher. As currently specified, the threads do not fluoresce under ultraviolet illumination; they are not visible in reflected light but are clearly readable to the unaided eye in transmitted
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light. The committee recommends that the position or width of the thread, which currently is essentially the same for all denominations, be varied by an obvious amount to permit denomination discrimination on the basis of position or width alone. In addition to their assistance to the casual viewer, such changes would assist in machine recognition.
A change in position would have to be carefully designed to avoid occlusion by another feature, such as a printed image. The center of the note should also be avoided, since that is where bills tend to be folded. As an alternative, the number of threads could be varied depending on the denomination. Both the wider thread and the incorporation of more than one thread raise concerns about creating weak zones in the substrate. Analysis would be required to determine if delamination and reduced note durability would result from these changes.
The committee was shown an example of a forged note with a simulated security thread, complete with microprinting. Though this note was not fully convincing, one cannot assume that the thread as currently employed will deter the dedicated professional counterfeiter. However, it is highly effective against the casual photocopy, which does not copy the thread.
Two enhancements to polyester security threads have been incorporated in foreign currencies. A windowed thread is used in British, German, Turkish, and Bahrainian currency, while Finnish notes use an imbedded thread with holographic printing (Haslop, 1993a). The current supplier of security paper to the BEP could implement a windowed thread following some development effort (Crane, 1993).
The security thread could be enhanced by combining it with other features. For example, if the thread were overprinted with characters using a photoluminescent ink, the characters could potentially be made to appear obvious on a reprographic copy. There are many potential combinations of other features that could be used to enhance the security thread. These should be studied for long-term implementation. The experiences of other countries in similarly enhancing their security threads should also be closely monitored.
Watermarks
Watermarks have been used in paper since handmade papers were produced in Italy at the end of the thirteenth century. It is estimated that some one million different watermarks were used before the introduction of machine-made papers in the nineteenth century. Watermarks have been widely employed for centuries as a means of marking high-value documents. For instance, authentication of rare prints and drawings often involves the study and identification of the watermarks contained in the substrate.
Watermarks may be introduced by bent wire devices in cylinder-mold paper machines, embossed in the wet paper with a dandy roll in a Fourdrinier paper machine, or impressed on the dried paper. Simulated watermarks may be printed on paper with fatty materials (Kühn, 1986).
The image in a watermark is formed by local variations in paper density becoming visible in transmitted light. The watermark may also be detected in transmitted light as a variation in the thickness of the paper. There are two types of watermarks. “Non-localized” ones that are placed in generalized locations throughout the substrate with no particular reference to other features; and “localized” or “registered” watermarks that are placed in a specific location
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within a printed image.
Watermarks are widely used in selected denominations of most of the world's currency. They were used in U.S. currency from 1869 to 1879 as part of a campaign to halt widespread counterfeiting that developed during the Civil War. Though watermarks are highly resistant to copying, they are not easily observed under difficult lighting conditions and can be simulated. However, watermarks can be designed to make high-quality simulations difficult. Should different watermarks be used for different denominations, they would introduce an added deterrent against “raising,” that is, bleaching a low domination bill and printing a higher denomination bill on the bleached substrate. The introduction of watermarks to U.S. currency was recommended in the previous National Materials Advisory Board report. The current supports committee supports that recommendation.
Tinted Substrates
A yellowish-green color tint is currently specified for all U.S. currency denominations. Such pale tints are difficult to reproduce accurately in most reprographic systems, are readily recognized, are easily machine read, and do not add to the cost of the paper. The use in U.S. currency of a pale tint that is difficult to reproduce serves as a visible deterrent. While the use of different tints for the several denominations and the general use of color, or selectively enhanced features in the unprinted stock, is discussed later in this chapter, it should be noted that tints can improve the effectiveness of other deterrent features. Tinted substrates are being used by many other countries, among them Mexico, Thailand, and Japan (Haslop, 1993a).
Paper Furnish Additives
The BEP has been offered a wide range of additives to the paper furnish that have the potential to increase the security of the paper substrate. Among them are planchettes, enhanced fibers, optical fibers, taggants, and particles with special properties. The enhancements for fibers and planchettes include: optically variable iridescence, dichroism, metamerism, microprinting, fluorescence, and phosphorescence. Since the quantities added would be very small (for example, the current BEP specification calls for 0.31 kg of red and blue fibers per 1,000 kilograms of fiber furnish), such additives offer low-cost deterrent possibilities. However, additives in these small quantities would be barely noticeable to the casual observer.
Fibers that are simply colored could be readily reproduced by high-quality copiers. Many other possible enhancements are discussed elsewhere in this chapter. The addition of small amounts of enhanced fibers (e.g., plastic optical fibers), or combinations of variously enhanced fibers, for example, may play a significant role in the random pattern/encryption concept, as discussed in a later section.
Fibers or particles that selectively emit or absorb light at the same wavelengths used for scanning or copying can produce obvious forgeries, because the copier or printer will yield spots or lines on the copy that are white, black, or unevenly colored. These are discussed below. A technical discussion of the chemical aspects of these features is present in the section, Inks for Printed Features later in this chapter.
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Counterfeit Deterrence Incorporated in Copiers and Printers
The committee has concluded that color copiers and color printers operated by the casual counterfeiter present the greatest counterfeiting threat. (See Chapter 2 and Chapter 3.) One approach to discouraging such opportunistic counterfeiting involves making the equipment less “friendly” to use. Two strategies being pursued are for the equipment to recognize banknotes and fail to reproduce them and for each copy from a particular machine to print a covert, traceable code in the image area of the reproduction.
Currency Recognition System
One manufacturer of advanced color copiers has developed and installed in its latest copiers, a first-generation system to automatically identify an attempt to copy certain banknotes (Tsujita, 1993). If the equipment detects a forgery attempt, it prints a black or blank copy and can be programmed to then shut down until it is reset by a repairman.
The detailed implementation of this anti-forgery approach has, understandably, not been presented in full detail. It is, after all, a security measure, and complete disclosure would leave the system vulnerable to compromise. Since it is a technological solution to a human problem, the solution is not likely to be perfect. It could however be reasonably effective for some period of time, particularly against the threat posed by the casual counterfeiter. But eventually any purely technological solution is likely to be compromised through development of some countertechnology.
This forgery detection and prevention system is, in effect, an expert system that includes software and hardware components (Canon, 1990) 13. The input information to the software is provided as a byproduct of the successive red, blue, green, and brightness scans. The scans provide a rough location of the position and orientation of the bill, followed by a refinement that includes the location and identification of important features on the bill. Statistical information is computed regarding the distribution of colors and feature sizes (possibly linked with color).
The example stated in the patent involves the detection of a specific Japanese banknote. The present system can reportedly store the data for four samples of each of eight different currencies; that is, 32 separate images. Therefore not all possible denominations of all possible currencies will be contained in the stored detection set. It is not known whether the samples stored in each machine are identical. Features have been included in the design of the electronics to prohibit operation of the copier if the forgery detection feature is disabled. However, a drawback for any technological approach to forgery detection is that once the rules are known, possible countermeasures can be developed to evade the detection algorithm.
13
The patent describes the form scanning operations used to determine if a forgery is being attempted. The first scan detects the approximate position of the note. The second scan determines the exact position and oventation of the note. The third scan calculates the expected position of the seal using data from the previous scans, and then determines if the seal is present at that position. The fourth scan produces a black full overprint of the note image if the third scan concluded that a forging is being attempted.
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There a number of unknowns. The committee does not know the extent to which this forgery detection process is successful. Reports are that it does work under a number ofunidentified conditions. (Legal considerations prohibited field testing of the feature by individual committee members.) This committee did not receive any information as to the efficiency of the process against simple countermeasures. Since the print engines in color copiers will also function as computer-driven output devices, it is not clear what degree of protection will be provided by the forgery detection feature in computer printers. Also, the degree to which the technology will be made available to other manufactures is not known.
The number of false alarm detections of currency will certainly become an issue. The cost of these machines is significant enough that no user will purchase a system that fails to copy any range of materials that “look like” but are not currency. Market forces will eliminate any feature that diminishes the usefulness of the copier. In addition, it is not known how well the feature can detect attempts to copy an already counterfeit (and thus not perfect) banknote.
In the opinion of the committee, the copier manufacturer is to be congratulated for this technological achievement. In the short term, the currency recognition feature will probably serve as a deterrent for the casual counterfeiter as a result of the knowledge about the anticounterfeiting feature. The committee, however, thinks that this feature will not be a long-term solution to the copying problem. Any well-defined technological detection scheme can probably be unwrapped by a technological solution. It is not likely to deter a technically knowledgeable, determined professional or casual “hacker” counterfeiter.
The present copy-protection scheme is a promising start. As electronics continue to grow cheaper and more capable, it is likely that more sophisticated schemes for recognizing attempts to copy currency will be made. Since the committee's concern is the U.S currency, it is interesting to note that good copying of the colors in the present currency are reported to be more difficult than that of some of the varicolored currency of other countries. Post-copying addition of simulations of such features as metallic or variable inks seems possible and can likely be done successfully. The use of metameric ink to “fool” the copier is not likely to be successful in the long run, as market forces will force development of techniques that are resistant to metameric problems in non-currency copying.
Consideration should be given to requiring the application of this technology to all advanced color copiers and printers, as other countries are considering. That depends, of course, on whether the patent holder is willing to license at least some aspects of the technology or if an alternative approach can be found that would be made widely available. Also, the addition of appropriate electronic components to all advanced color copiers and printers could increase the price of the low-end models significantly enough to be outside the range of the feasible.
The usefulness of this approach could be enhanced if many nations adopted the same unique feature on their banknotes that would trigger the currency recognition system. In addition to easy detection, such a feature should not require extensive pattern-matching algorithms to match-up scale, geometric orientation effects, etc. A fractal-based self-similar pattern, such as is shown in Figures 4-12, may be useful. The U.S. Treasury Department could take the lead in lead in defining the problem and securing international cooperation in this regard.
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It is important to note that the color copier will fail to copy correctly such features as metallic inks, color-shifting inks, and holographic types of features. It is possible to consider machine detection schemes that are capable of discriminating such features on currency and detecting probable attempts to carry out forgeries. The result of a copy operation will be to record whatever optical image of the variable feature is presented through the copier which will necessarily be incomplete and readily detected.
Copier/Printer Identification System
A potentially important feature on some advanced copiers is the encryption of the machine serial number at several locations on all of the copied material. A microdot pattern is used to encode the machine number in every copy that is made. Detection and reading of this encoded microdot pattern require special techniques that must be implemented in the laboratory. The presence of a traceable origin of each copy will probably deter some copying and would make tracing the origin of copied currency possible14.
Consideration should also be given to extending this technique to color printers, not just electophotographic printers (e.g., ink-jet printers). This may require the addition of additional pre-printing computational processing steps, resulting in a requirement for increased computational power. The cost effectiveness of such a requirement must be closely examined.
Features Used by Other Countries
During its deliberations, the committee considered more than forty types of features that were deemed either to offer an aid to detection of counterfeit currency or to act as a deterrent to counterfeiters. The debate had to take place mainly in the domain of the former, since there are relatively easy measures of success for detection —either in the public marketplace or by official government agencies —whereas it is more difficult to prove a negative in the domain of the latter (i.e., whether due to incorporation of any specific feature, counterfeits have not shown up in circulation).
Of the long list of special features (a described in detail throughout this report), all but about a dozen are already incorporated in world currencies, although some have been introduced only relatively recently (e.g., plastic substrates in Australia) or have been announced to be imminent (e.g. kinegrams in Australia now, in Switzerland in 1995). Thus, at first sight, it might appear that there is a considerable body of experience to draw from, but in actuality there are few quantitative facts. Obvious and intuitive special features such as holograms may have defeated color copiers and other forms of electronic printing but could be relatively easy for proficient counterfeiters to simulate otherwise. They may even be counterproductive in the sense that they may reduce the practical life of the note or focus attention on a single feature of the note. On the other hand, color-shifting inks —now used
14
The committee realizes that other public policy issues will be raised by this capability. The perspective here is purely from the standpoint of counterfeit deterrence.
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by many countries—are more subtle in appearance but defeat color copiers and at this stage would seem to be more difficult to counterfeit by other means. The trade-off would thus seem to favor color-shifting inks, but there are no readily available data to support this conclusion. The situation becomes further complicated by the classification into visible and hidden features. For example, Dutch currency has incorporated visible bar codes, whereas Great Britain uses these codes in hidden form, principally as an aid to the automatic sorting of notes by banks. Most “smart inks” are not obvious unless detected by means of an appropriate physical property, such as fluorescence, phosphorescence, iridescence, and magnetic properties. There are varying degrees of difficulty in copying or simulating these inks using existing technologies. The inks currently used by various countries, but again with little quantitative evidence of effectiveness.
The majority of features deemed attractive for special consideration by the committee have typically already been incorporated in one or more currency (or related documents). On the other hand, technical approaches that appear promising for future research and consideration (e.g., optical fibers in paper) have not yet been incorporated in any known currencies and so there is no practical experience on which to draw.
The overall conclusion is that whereas long lists can be drawn up of currencies incorporating a variety of smart features, there is very little evidence of quantitative effectiveness, or for that matter of sharing any practical experience between countries. Ironically, it is the existence of new emerging global communication technologies (electronic networks and output devices) that presents the opportunity for prospective counterfeiters and that may pose a much more serious problem as these technologies evolve. Just as a single, new high-quality color copier may cause simultaneous counterfeiting problems worldwide, the power of a collective deterrent strategy rather than ad hoc design changes by individual countries will probably become increasingly important.
A handful of nations print their own currency—these are typically the more economically advanced nations—while the remainder are served by a very small number of private printing companies. In that sense, there are only relatively few “independent” blocks of data/experience, and there are existing collaborations between some of these blocks in certain common currency matters. It is important to increase the degree of sharing of counterfeiting/deterrence information.
Other U.S. federal agencies are concerned with secure documents. These include the Postal Service (e.g., postal money orders), State Department (Passport Office), Agricultural Department (e.g., food stamps), and so on. Increased sharing of ideas and experience would be mutually beneficial. Thus it would seem there are obvious avenues for greater sharing of experience and for a collective approach to research in detection and deterrence in the future.
RECOMMENDATIONS
Although there are many new features that can be used to deter counterfeiters, the BEP should continue to utilize intaglio printing, the security thread, and the current substrate material as methods of deterrence against “classical” printing technologies and present day reprographics. In addition, future banknote designs should incorporate additional visible
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features to serve as deterrents against counterfeiting and as a means for rapid visual authentication. If analysis shows it is cost-effective to do so, some of these visible features could be incorporated into a banknote and their existence not publicly disclosed until they are needed to thwart a new counterfeiting threat.
The BEP should implement a system of complementary features on each banknote that create added complexity for simulation by all levels of counterfeiters. They should not, however, constrain their design by a requirement that the same set of counterfeit-deterrence features be on all denominations of bills. And although multiple features rather than a single dominant feature should be present on each banknote, the number of announced features should not be so great that it overwhelms the user or does not allow space for future feature incorporation.
The BEP should carry out a redesign of U.S. banknotes to include the recommended features, making such changes in appearance as are necessary to produce a new series of notes that effectively and efficiently incorporates these advanced counterfeiting deterrents. By a wide margin, most banknotes in circulation are genuine. All things being equal, deterrent features that would cause a counterfeit note to look significantly different from a genuine note would probably be more useful to the average citizen than a feature that caused a genuine note to be authenticated upon detailed inspection. On the other hand, a specific machine-detectable feature incorporated in a genuine note would be more useful in a currency-authentication device.
The recommended features fall into three categories: near term, intermediate term, and long term. Within the categories, the deterrent features are not prioritized because of insufficient data relating to implementation issues and the realization that no single feature is adequate protection from even casual counterfeiting.
The committee recommends incorporation of at least some of the following visible features in the near term:
color-shifting inks for printing;
moiré (alias-generating) line structures, with color added as necessary to enhance the effect;
security thread modifications—for example, location or width based on the denomination;
variable-size dot patterns, with color added to enhance the effect; and
localized watermarks.
Incorporation of at least some of the following features, requiring inexpensive visual aids for detection at the point-of-sale, are recommended for the intermediate term:
infrared inks for printing;
optically active coated fibers and particles embedded in the substrate; and
photoluminescent inks for printing.
Longer-term plans for advanced deterrents (listed in alphabetical order) should include additional development and understanding of the following features:
diffraction-based holograms and related devices;
embedded zero-order diffraction gratings;
laminated paper substrates with selected features;
metallic or specular woven security features;
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optical fibers embedded in the substrate; and
random pattern encryption methods.
For the far term, the BEP should continually assess fundamental advances in the chemical, applied physical, and biological sciences for developments that are applicable to innovative deterrent features. Assessment of research in psycho-physics would also be pertinent since a better understanding of how people perceive visible features may provide insight into the selection of the “best” features.
Before any new counterfeit-deterrent feature is implemented, it should be evaluated by adversary-analysis experts to determine how readily it can be defeated. This process would be aided by having a means to quickly produce currency with appropriate design changes.
There are other elements of a deterrent strategy that can be implemented. To begin with, counterfeit-detection education should be emphasized for point-of-sale persons as a priority, and then for the public at large. Potential incentives that would encourage the public to turn in counterfeits should be closely studied to determine which would be effective and not subject to abuse15.
Industry should be encouraged to develop effective point-of-sale aids to assist in banknote authentication. Efforts that will lead to a high degree of authentication, particularly for the higher denomination bills, should be continued. These may involve synergistic combinations of visible and hidden covert features that could be related in some way, such as through a public key encryption system.
The Department of Treasury should encourage U.S. legislation to require source identification to be embedded in images produced by new copier and printer systems capable of producing color counterfeit banknotes. In addition, the department should strongly encourage the use of sensors built-into color copier/printer systems that can recognize and inhibit banknote copying. For this approach to be most effective, a unique, high signal-to-noise ratio feature universally applied to currency should be identified and developed, possibly in conjunction with other nations.
15
The committee believes that counterfeiting should not be a “victimless” crime, since the fear of a loss does provide the public with some incentive to examine banknotes.
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