SECURITY PRINTING APPARATUS AND METHOD
This application is being filed as a PCT International Patent application in the name of F. Charles Baggeroer, a U.S. citizen, and Ruediger Guenter Kreuter, a German citizen, applicants for the designation of all countries, except the US.
Background of the Invention
Counterfeiting of identity and financial transaction documents is a long-standing problem. Recent technological advances in the area of digital reprographics are further exacerbating this problem. It is now easy for criminals to purchase high quality color digital printers for paper or plastic substrates. The images printed with these devices often exceed the resolving power of the unaided human eye. Document issuers have responded to these attacks with a number of defenses. The defenses are targeted at one or more levels of examination, the untrained lay person, the trained field examiner, and the forensic examiner. The majority of these defenses can be grouped into one of three classes - optical variable technologies, covert materials, and high-resolution security printing techniques. Each has advantages and disadvantages. The present invention is concerned with the last category - security printing techniques.
Traditional security printing uses very high-resolution pre-press systems. The high spatial resolution of such systems permits creation of designs that can incorporate techniques such as curved lines or line segments with constantly varying width, intricate fine line patterns (guilloches), and lines or dots having variable spatial frequency. Lithographic printing plates are then produced with these patterns. Such plates can be created using a photographic process or with a laser that etches away material from the plate.
Such security printing techniques will frustrate commercially available raster mode printing (dots printed at fixed spatial frequency) for many years. However, this technique has a number of limitations. One limitation is the marginal training and motivation of the first level examiner. First level examiners are not easily motivated to inspect the documents, and even if motivated may have difficulty making a determination regarding the document's validity. Another limitation is that, for a second level examiner, verifying the document's validity based on such patterns may require delicate or expensive equipment.
Yet another limitation of preprinted security patterns is their inability to include variable, unique information. When a fixed security design is used with a large number of documents the potential payback to a counterfeiter increases. Ideally, a security design would have elements uniquely linked to a specific document.
Laser printing on plastic transaction cards is a known art. Datacard Corporation introduced a system in 1982 that used a laser as part of an electrophotographic process that transfeπed toner to the surface of a card. However, this system lacks spatial resolution needed for security printing. At approximately the same time Giesecke & Devrient GmbH introduced a laser engraving process for plastic cards. This system is capable of variable printing, but cannot achieve the security printing described herein.
The present invention addresses each of these limitations in addition to other novel features.
Summary of the Invention
The present invention relates to a security printing technique that combines classical high-resolution security printing with direct printing of variable data on security documents.
The term "security documents" is used herein in its broad sense. For the purposes of the present invention, a security docmnent is any document with security features for facilitating the distinction of genuine or proper documents from invalid or counterfeit documents.
Such a definition may include a wide variety of specific documents. For example, the present invention may be particularly advantageous with respect to transaction documents. Transaction documents are those documents that enable or facilitate transactions of various sorts, including but not limited to financial transactions and such non-financial transactions as border crossings, travel within or between nations, etc.
Specific examples of financial transaction documents include, but are not limited to, bank cards, credit cards, negotiable or non-negotiable bonds, and even cuπency. Specific examples of non- financial transaction documents include, but are not limited to, passports, visas, travel permits, border passes, and security badges or identification cards.
However, the present invention is not limited to transaction documents only. The present invention may be equally suitable for use with other documents wherein security printing is desirable, including but not limited to
permits such as driver's licenses, collectables such as trading cards, and certificates indicating proper licensing or authenticity.
For purposes of clarity, the invention is generally described herein using the example of a plastic transaction card as the security document. However, as noted above, the invention is not limited to transaction documents only. Furthermore, although a variety of security documents may use plastic cards as substrates, this is exemplary only. The invention is not limited only to security documents using plastic cards as substrates. Other substrates that may be suitable include, but are not limited to, paper, cardboard, and plastic films. In one embodiment of a process in accordance with the principles of the present invention, a laser engraving process is utilized which "writes" using a series of overlapping dots at very high resolution, currently finer than 0.005 mm spacing. The laser beam is directed to move from one position to another in piecewise continuous line segments, such motion being otherwise lαiown as vector mode. It is envisioned that the laser beam will be directed using software running on a computer.
However, it will be apparent to those of skill in the art that this method is exemplary only, and that other methods of producing the security writing may be equally suitable. In particular, the invention is not limited to etching or engraving of the substrate. Other printing processes may be equally suitable, including but not limited to processes that produce marks that are deposited on the surface of the substrate, i.e. inlc jet printing, and processes that produce marks beneath the surface of the substrate, i.e. by using a light beam to mark a photosensitive film within a substrate.
Using the combination of vector mode and high resolution various forms of card unique security printing can be created. For example:
1. Information, typically alphanumeric text, can be written at continuously changing point size, from sizes readable with the unaided eye to "micro-printing" viewable only with magnification. The details regarding character size can be unique for each card or group of cards.
2. Information can be written following customer definable curves, including but not limited to sinusoidal, elliptical, parabolic, hyperbolic, functions etc.
3. Lines and shapes can be created using continuously changing line widths.
4. Information can be written at various depths, such as raised or inset lettering or information totally contained within the card structure. *•
It will be apparent to those of skill in the art that these security features are exemplary only, and that other features, including but not limited to other alterations of text and images, may be equally suitable for use as security features.
In addition, it is noted that although some of the security features printed on a given document may be unique to that document, others may be printed that are similar or identical for two or more documents. For example, a passport might include one or more security features that are unique to that individual passport, while also having security features that are common to all passports issued in a given month or year, all passports from a given province or city, etc.
With such security printing document examination at all levels is facilitated and encouraged.
Simple first level examination is facilitated because the security feature is easy to describe, has a unique appearance, can be easily viewed under various ambient conditions and is permanent. The variable character sizes encourage examination. Because the marking process is affected during personalization, cardholder unique information can be imparted to each card. The variable data can be related to infonnation applied using other technologies, further discouraging alteration.
Simple second level examination is also facilitated, A transparent template can be prepared which outlines the location and geometries of the variable information. Since the issuer can define the location, curvature, and character size, each group of cards produced will be unique to that template. These variables, in effect, serve a similar function to encryption keys.
Because the information is imparted during personalization it can be algorithmically or crypto graphically linked to other card data. For example, a card having a serial number thereon may use the serial number, or a portion thereof, in the algorithm, even if the serial number itself is not transfoπned by the algorithm.
Visible data on the card that is used in this fashion is not limited to text. For example, in a document having a graphic image such as an identification photograph thereon, information that is present within the graphic image, i.e. biometric data from a face shown in the image, data regarding such properties as colors, shades, and shapes present in the image, etc. could be utilized in the algorithm.
Furthermore, data that is present but not be visible on the card may also be used for the algorithm. For example, data in microchips, magnetic stripes, or other data storage structures may be used in the algorithm.
Information regarding the relationship between the linked data can be restricted or kept secret.
Brief Description of the Drawings
Figure 1 is a lattice showing letter height and distance for non- distorted text.
Figure 2 is a lattice showing letter height and distance for text distorted by enlarging the center and shrinlcing the ends.
Figure 3 is a lattice showing letter height and distance for text distorted according to a trigonometric function.
Figure 4 shows an example of text distorted by enlarging the center and shrinking the ends. Figure 5 shows an example of text distorted by enlarging one end and shrinking the other end.
Figure 6 shows an example of text distorted according to a trigonometric function.
Figure 7 shows an example of text with detailed internal structure at low magnification.
Figure 8 shows a portion of the text of Figure 1 at greater magnification.
Detailed Description of the Preferred Embodiment
An exemplary embodiment of a security document in accordance with the principles of the present invention includes a substrate, with at least one transformed image formed on the substrate. The transformed image is a product of a mathematical algorithm applied to an original image to transform it.
The transformed image differs from the original image in at least one geometric feature, that feature being produced by the mathematical algorithm. This geometric feature is also refeπed to herein as a security feature.
The geometric feature may vary widely from embodiment to embodiment. Suitable geometric features include, but are not limited to, changes in shape, size, aπangement, internal structure, color, and shading. The geometric feature may or may not be immediately obvious, and indeed may or may not be visible to the unassisted eye.
It is noted that the new feature produced by the transformation need not represent some gross structure or portion of the transformed image that has been added to or subtracted from the original image. That is, it is not necessary to add per se shapes, colors, etc. not present in the original image, or to delete per se shapes, colors, etc. that are present in the original image.
For example, a line of text or other feature may be present in both the original and transformed images, and will not necessarily include additional characters in the transformed image. A geometric feature is considered to be produced so long as the transformed image differs in some identifiable way from the original image, and so long as that difference is produced by the mathematical algorithm. The particulars of the geometric figure or figures produced by the algorithm may be obvious or subtle, and may vary widely from embodiment to embodiment.
Similarly, the range of suitable original and transformed images may be extremely broad. Any image that can be processed into another image by a mathematical algorithm may be suitable as an original image. Similarly, any image that may be produced from another image by use of a mathematical algorithm may be suitable as a transformed image.
Laser engraved texts have significant properties that differ from those of texts produced by other printing techniques. Some of these properties can be easily observed without instruments, while other properties can be only checked in a laboratory. For example:
1. Laser engraving produces a mark that extends into the volume of the substrate, rather than only affecting the surface of the substrate.
2. Because the print is produced by reshaping of the substrate rather than by applying an ink or other marking material, the print is as resistant to environmental hazards such as water and hydrocarbons as the substrate is. 3. The text may be engraved in such a way that it may be sensed tactilely as well as visually. The resolution of laser engraved texts and graphics is determined by the scanner and the optical parameters of the laser beam and the lenses. The theoretical minimum spot size is determined by the wavelength of the laser, which presently limits spot sizes to a minimum of about 1 μm. In practice, the minimum spot size is presently limited to a value of about 50 μm, depending on the divergence of the laser and the f-Θ objective used (for a focal length of f = 100 mm and a divergence δ = 0.5 mrad, spot size « δ • f). Thus, the maximum print resolution
available therefrom is approximately 500 dpi. The resolution of available scanners is less than 2 μm, therefore this does not further limit the resolution of the print. The resolution of print that may be generated by laser engraving increases with decreasing laser wavelength and also with decreasing laser beam divergence. It will therefore be apparent to those with knowledge in the art that this engraving resolution is exemplary only, and that other resolutions may be equally suitable. In particular, it will be apparent that higher resolutions that may become available due to improvements in laser technology may be equally suitable for use with the present invention. It is envisioned that the texts that are to be engraved by the laser, printed, or otherwise formed may be modified by mathematical transformations before the engraving takes place. Depending on the particular transformation, the text may be visibly changed, for example by a distortion of the text line, or the text may be changed in a manner that is not visible to the unaided eye, as by adding a subtle modulation in the print properties.
Whether the changes are visible or not, the properties of the letters (i.e. size, shape, internal patterns) may be changed continuously. The variations need not be stepwise between the different letters. The variation may be continuous, even within a single letter. The continuous distortion of the letters may be compared to a projection of the letter onto a three dimensional arched surface.
In Fig. 1 to Fig. 3 several exemplary schemes for distortion of text are illustrated. Fig. 1 shows a non-distorted lattice, with a constant x/y ratio for the letters. Every point of the lattice coπesponds to a point in a text line. The transformation of this lattice effects a bending of the lines, and a consequent distortion of the text.
In Fig. 2 and Fig 3 transformed lattices are shown. In Fig 2 the letters at the end and at the beginning of the text are reduced in size, while in the center the letters are increased in size. In Fig. 3, the size of the letters changes periodically, following a trigonometric function. As shown, only the horizontal lines are bent, while the horizontal lines are straight lines. However, it will be apparent to those with skill in the art that these transfonnations are exemplary only, and that other transformations may be equally suitable. In particular, transformations where either the vertical lines are bent in addition to or instead of the horizontal lines may be equally suitable. Similarly, it will be apparent that a variety of spatial properties may be varied for a particular transformation. For example, for a periodic trigonometric function as shown in Fig. 3, variable parameters may include but are not limited to the phase Φ, the frequency v of the function and the maximum and minimum height amplitudes.
Moreover, the particular transformation used can change for every laser engraving process. In particular, parameters for the transformation may be determined from the text to be printed. That is, the transformations applied to the layout of the text (whether visible or invisible to the eye) changes in dependence on the contents of the text. For example, the text may be transformed according to an algorithm that is dependent on the numerical values of the ASCII codes for the letters to be printed. In such a case, duplication of a particular set of letters could only be performed by someone with by the knowledge of the transformation algorithm. It will be apparent to those with skill in the art that an ASCII-based algorithm is exemplary only, and that other algorithms may be equally suitable.
Figures 4-6 show exemplary samples of transformed text. For reference, the distance between two tick marks is 0.1 mm.
It is also envisioned the transformations may produce features of the text that are not directly observable. For example, as shown in Figs. 7-8, internal structure may be added when the letters are enlarged by the transformation process. In this case, as is visible in Figure 7, line structures in the letters cannot be resolved without optical instruments. The human eye will only detect a change in the gray scale of the letter as the fine line structure varies in density. However, if the letters are magnified as in Fig. 8, a line structure characteristic of the transformation algorithm become visible.
It will be apparent to those with skill in the art that this particular algorithm for producing added structure is exemplary only, and that other algorithms that add or modify structure differently within graphics or text may be equally suitable. In particular, an algorithm that is not based on letter size may also be suitable.
A transformation of text contained in a pixel file can be expressed as a bending of the orthogonal coordinate axis of the pixel field. The transformation of the coordinates can be written as: P(x„ y,) - P(ξ„ η,)
wherein x, is the ith value of coordinate x y, is the jth value of coordinate y P(x„ y,) is a pixel at coordinates x,, y, ξj is the ith value of coordinate ξ r\} is the jth value of coordinate η P(ξl5 r|j) is a pixel at coordinates ξ„ ηj
ξi = fι(Xi, Vj) η. = f2(χi, yj)
That is, the original pixels P(XJ, yj) in the x-y axes are used to generate pixels P(ξi, r|j) in the ξ-η axes, where each value of ξ and η is created by functions fi and f2 of the respective values for x and y.
It will be apparent to those of skill in the art that this transformation is exemplary only, and that other transformations may be equally suitable. In particular, transformations to and from coordinate systems with more than two coordinates, and to and from coordinate systems other than the Cartesian coordinate system illustrated above, may be equally suitable.
It is envisioned that such a transformation could be performed in real time by a conventional personal computer.
For example, for such a conversion of a suitable *.pxl type file, the following steps would be performed:
1. Conversion of a * .PXL file of the size (n, m) to a bit array of the size (n, m).
2. Coordinate transformation of the aπay of the size (n, m) to an aπay of the size (v, μ) as determined by the functions fi and f2. 3. Interpolation of non determined bits.
4. Conversion of the bit aπay of the size (v, μ) to a *.PXL file of the size (v, μ). It will be apparent to those of skill in the art that this conversion process is exemplary only, and that other conversion processes may be equally suitable. In particular, files other than *.pxl files may be equally suitable.
It is envisioned that software for applying a particular algorithm for coordinate transformation may be distributed in at least two formats.
First, the algorithm may be integrated in the source code, such that it can not be changed by the user. In this case the algorithm can be checked during creation to verify that it will work for every pixel file.
Second, the software may be written so that one or more parameters of the algorithm (and therefore the representation of the distortion) can be changed by the user. The parameters could be read from a separate file created by the user or by a third party, for example. In this case, the parameters may be set by the user to accommodate a particular need. However, a parameter check would have to be performed for custom parameters, because a reasonable result is generally obtained only for a small parameter range. For example, it is possible to generate transformations that could not be conveniently displayed on the substrate due to size,
complexity, etc., or that would render transformed text unreadable. It is envisioned that the transformation software would itself include provisions for performing a parameter check, and that a suitable graphic user interface would be developed to assist the users. However, it will be apparent to those of skill in the art that this aπangement is exemplary only, and that other aπangements, in particular other interfaces and separate software or other tools for performing parameter checks, may be equally suitable.
The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.