Abstract:
A system for storing information including a first partial portion of a printed marking, and a second partial portion of the printed marking. The printed marking comprises first information in a first information storage format. The first partial portion is printed with a first ink. The second partial portion is intermixed with the first partial portion to form the printed marking. The second partial portion is printed with at least one second different ink. The second ink comprises a metameric ink which becomes excited when exposed to an excitation source such that the printed marking contains second different information in a second different information storage format which can be read when the printed marking is exposed to the excitation source.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a printed indicium, marking or document and, more particularly, to a printed indicium, marking or document which is printed with at least two different inks.  
         [0003]     2, Brief Description of Prior Developments  
         [0004]     Printed documents carry information using at least one predefined set of characters (symbology). An example of symbology used to create documents intended for human reading is an alphabet. Documents intended for machine readability may use barcode symbology for example. Glyphs and other methods of hiding information in images (steganography) are known to exist. Cryptographic methods to ensure authentication and integrity of documents are also known to exist.  
         [0005]     In some instances, important printed documents have to demonstrate that they were created by a specific entity (such as a person or organization), possibly on a specific date. A common method of authenticating the source of a document is a digital signature. A digital signature is a method of adding a group of characters to an existing document using cryptographic algorithms and private codes. The result of adding a digital signature to a printed document is an additional group of symbols which are (in known implementations) visible like the rest of the document. These symbols do not carry any of the original message (payload), but they can be used to determine if the payload was created by a specific entity, on a specific date and that it was not altered since it was created. In most cases, the recipient of a printed message is interested only in the payload. However, on occasions, the recipient needs to verify the digital signature to confirm the source of the document and its integrity. In most cases, users of such documents would prefer to “not see” the codes used for authentication and integrity. These codes are considered by many to be “ugly” and they distract the reader from the message being conveyed by the document.  
         [0006]     Similarly, some documents use error detection and correction codes to increase the chance of retrieving the document payload, such as when some of the printed areas are not readable due to miss-handling (e.g. dirt, ink smudges, printing defects). Adding error detection and correction codes to a document payload also involves computing and printing characters in addition to the intended message (payload). Like digital signature codes mentioned above, users also prefer not to have to “see” these codes.  
         [0007]     Printing indicium, such as linear or 2D bar codes or mail piece indicium, with one ink limits the information capacity of the indicium and also does not allow embedding of covert information. Barcodes are used in many applications for the identification, tracking, and tracing of objects, letters, or packages. Some applications require only very basic information about an object (identity or destination) while other applications require detailed information about an object (e.g. postage paid, origin address, postage meter number, sender, addressee, destination address, weight, date, contents, batch number). Barcodes are also used extensively for the identification of objects for sale; for example the Universal Product Code (UPC), and in many other applications. Such barcodes could, in principle, be expanded to include data about batch numbers, production dates, or expiration dates to aid in product recalls and rotation of product inventory.  
         [0008]     Introduction of additional indicium information can be hindered by several factors including: real estate available on the object; existing standardized specification precluding expansion (e.g., PostNet is set as 12 digits); resolution of existing readers and printers; expense and logistics to retrofit existing readers and printers; need for printed indicium schemes (such as a barcode scheme) to conform to the least common denominator user.  
       SUMMARY OF THE INVENTION  
       [0009]     In accordance with one aspect of the present invention, a system for storing information is provided including a first partial portion of a printed indicium, and a second partial portion of the printed indicium. The printed indicium comprises first information in a first information storage format. The first partial portion is printed with a first ink. The second partial portion is intermixed with the first partial portion to form the printed indicium. The second partial portion is printed with at least one second different ink. The second ink comprises a metameric ink which becomes excited when exposed to an excitation source such that the printed indicium contains second different information in a second different information storage format which can be read when the printed indicium is exposed to the excitation source.  
         [0010]     In accordance with another aspect of the present invention, a system for reading hidden information stored in a printed indicium is provided comprising a system for exciting portions of the printed indicium printed containing metameric ink; and a system for reading locations of the excited portions of the printed indicium relative to non-excited portions of the printed indicium in a machine readable information storage format to thereby read the hidden information.  
         [0011]     In accordance with one method of the present invention, a method of printing a printed indicium is provided comprising determining first portions of the printed indicium which are to be printed with a first ink and second portions of the printed indicium which are to be printed with a second different ink, wherein the first and second portions provide a first information; printing the first portions with the first ink; and printing the second portions with the second ink, wherein the second ink comprises metameric ink, and wherein positions of the first portions relative to the second portions provide a second machine readable information.  
         [0012]     In accordance with another method of the present invention, a method of authenticating a printed indicium is provided comprising reading the printed indicium using a first information reading format; and reading the printed indicium using a second different information reading format, wherein reading the printed indicium using a second different information reading format comprises exciting second portions of the printed indicium with an excitation source and determining locations of the second portions relative to first portions of the printed indicium.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The foregoing aspects and other features of the present invention are explained in the following description, taken in connection with the accompanying drawings, wherein:  
         [0014]      FIG. 1  is a system diagram of a system for producing a printed indicium or document comprising features of the present invention;  
         [0015]      FIG. 2  is a view showing text or indicium of one example of the present invention;  
         [0016]      FIG. 3  is a partial chart of hexadecimal representations of some of the characters shown in  FIG. 2 ;  
         [0017]      FIG. 4  is an example of the first few bytes of a signature calculated over the document shown in  FIG. 2  to be used with the document;  
         [0018]      FIG. 5  is a diagram showing sectioning of the characters of the example shown in  FIG. 2  for the signals shown in  FIG. 4 , and illustrating by emphasis the characters printed with two different inks;  
         [0019]      FIG. 5A  is a diagram showing the text of  FIGS. 2 and 5  as three separate illustrative lines of normal daylight text, only characters printed with the second ink, and only characters printed with the first ink, respectively;  
         [0020]      FIG. 5B  is a diagram showing the text of lines  19  and  20  converted to digital binary digits based upon presence of the first and second inks;  
         [0021]      FIG. 5C  is a diagram of the line shown in  FIG. 5B  with spaces removed;  
         [0022]      FIG. 5D  is a diagram of the line shown in  FIG. 5C  sectioned into signals and illustrating the signals generated from the groups of bits;  
         [0023]      FIG. 6  is a chart of intensity versus wavelength for two examples of Black Fluorescent Ink which could be used as the second ink;  
         [0024]      FIG. 7  is a diagram showing one example of a system for reading the printed indicium or document;  
         [0025]      FIG. 8  is an image of a form captured with a conventional camera or scanner using normal lighting conditions;  
         [0026]      FIG. 9  is an image of the form shown in  FIG. 8  captured with a UV camera or scanner with the document exposed to UV light; and  
         [0027]      FIG. 10  is the result of processing the images from  FIGS. 8 and 9  to extract the hidden second information used for authentication, integrity and/or redundancy of the document or first information in the document. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     Referring to  FIG. 1 , there is shown a system diagram of a system  10  for producing a printed indicium incorporating features of the present invention. As used herein, the terms “document” and “indicium” and “marking” are used interchangeably for purposes of describing the invention. Although the present invention will be described with reference to the exemplary embodiments shown in the drawings, it should be understood that the present invention can be embodied in many alternate forms of embodiments. In addition, any suitable size, shape or type of elements or materials could be used.  
         [0029]     One type of implementation of a method of the present invention can use Black Fluorescent Ink (BFI) in a printer  110  with two ink cartridges. One ink cartridge can print with regular black ink and the other cartridge can print with Black Fluorescent Ink (BFI). In alternate embodiments, the two inks could have any suitable color in normal daylight. In another alternate embodiment, more than two inks could be provided in the printer  110 .  
         [0030]     The present invention comprises a process of adding information (such as numeric information) to achieve document authentication, integrity and/or redundancy which may be performed in conjunction with other standard action(s) taken by the user during the process of creating and printing a document. For example, the determination of which element or character of a printed indicium or document to be printed with Black Fluorescent Ink (BFI) can be added to either the Save or Print operations during document creation. This can be transparent to the user.  FIG. 1  is an illustration of adding such information just before a Print operation. It is assumed that an initialization step has already taken place when user preferences and crypto-keys were configured appropriately.  
         [0031]     The user of the system creates a document, such as a text document. An example of a text document is shown in  FIG. 2 . This text is sent from the Word Processor  100  to be printed. A software module  102  can intercept the text and calculate which letters/characters will be printed with BFI. When using a standard printer, one may replace a color ink cartridge with a BFI cartridge. As a result, the software module  102  changes the ink of chosen letters. The system  10  can use a cryptographic sub-system  104 . The operating system  106  can send the information to the print driver  108  which sends the information to the printer  110 .  
         [0032]     The process of choosing which letters to print with BFI is described next. An example of hexadecimal representations  16  of the first few letters  14  of the text of  FIG. 2  is illustrated in  FIG. 3 . As further described below, these hexadecimal representations (or equivalent representations) can be used after the indicium or marking or document  12  is printed as partial input to algorithms used to calculate digital signatures, Message Authentication Code (MAC) and/or redundancy codes. The characters in the printed indicium or document  12  shown in  FIG. 2  can be read such as with a scanner and Optical Character Recognition (OCR) program. The software module  102  can calculate a digital signature, MAC or error correction codes using a numeric representation of the text. For example, as illustrated in  FIG. 4 , the first few bytes  18  of the signature calculated over the entire document could be “A2 34 94 36”.  
         [0033]     In the next step, the information that needs to be encoded into the document (in this example “A2 34 9F 36”) is used to decide which letters of the document will be printed with BFI; leaving the rest of the letters or characters to be printed with regular black ink. The result will be a document which will have a substantially same aspect as a document printed with solely regular black ink when looked at using normal light. However, under Ultraviolet (UV) light certain letters of the text will appear to have a different color.  
         [0034]     In  FIG. 5 , the characters of the text shown in  FIG. 2  are which are to be encoded with a digital or binary “1” were selected to be printed with BFI and are shown bold. In the actual implementation, the text under normal light will not be altered and bold will not be added to the characters printed with BFI ink; nor will there be any other visible aspect differences of the elements printed with BFI and elements printed with non-BFI ink in the document. Line  20  in  FIG. 5A  shows how the text would appear in normal daylight. Line  22  shows merely the letters printed with the second ink; the BFI. In particular, the letters are T, e, c, o, w, f, j, p, e, d, o, v, t, h, I and a. Line  24  shows the letters printed with the first ink; the non-BFI ink.  
         [0035]     Referring also to  FIG. 5B , the line of text is shown converted into a line  26  of digital or binary digits of “0” and “1”. “0” has been assigned to characters not printed with BFI; the characters shown in lines  19  and  24 . “1” has been assigned to the characters printed with BFI; the characters shown in lines  19  and  22 . Line  26  still shows the spaces between the words. Referring also to  FIG. 5C , the line  26  is shown without the spaces as line  28 . Referring now to  FIG. 5D , the digits of line  28  are sectored into four signals  30 - 33  of eight digits each and a remainder  34 . Each of the signals  30 - 33  symbolize one of the bytes  18  of the signature as seen below the signals (see also  FIGS. 4 and 5 ).  
         [0036]      FIG. 6  shows a chart of fluorescence intensity relative to wavelength of two examples  36 ,  38  of BFI ink which could be used with the present invention as the second ink. One of the examples  36  comprises a rare earth addition of CD380. Printing of postage indicium with a color metameric ink, such as a fluorescent ink or a phosphorescent ink, is described in U.S. patent application Ser. No. 10/692,569 filed Oct. 24, 2003, which is hereby incorporated by reference in its entirety. Dark color fluorescent inks (e.g., dual luminescent) are described in U.S. Pat. Nos. 6,827,769; and 6,793,723; and U.S. patent application publication Nos. US 2002/0195586 A1, US 2003/0005303 A1, and US 2003/0041774 A1, which are hereby incorporated by reference in their entireties. U.S. patent application Ser. No. 10/692,570, which is hereby incorporated by reference in its entirety, describes halftone printing and gray scale printing with multi-signal transmission ink. U.S. Pat. No. 5,153,418 discloses multiple resolution machine readable symbols. IR absorbing ink with IR absorbance could also be used.  
         [0037]     In one embodiment of the present invention, the first ink used to print the indicium or document preferably comprises a normal printer ink, such as a non-luminescent black ink as mentioned above for example. The second ink used to print the indicium or document preferably comprises a color luminescent ink, such as a fluorescent ink or a phosphorescent ink, such as described in U.S. patent application Ser. No. 10/692,569 filed Oct. 24, 2003. In a preferred embodiment, the first and second inks have a substantially same color in normal daylight when viewed by a person, such as black for example. Because the second ink is a luminescent ink, it can be excited by a radiation source, such as an Ultraviolet light, to read the second ink separate from other inks. In alternate embodiments, any suitable type of inks (such as metameric inks for example) can be used so long as the inks can be differentiated from one another, but preferably are substantially visually indistinguishable for each other in normal daylight conditions. With the invention, information can be encoded as described in U.S. patent application Ser. No. ______ , filed concurrently herewith (Attorney Docket No. F-942), which is hereby incorporated by reference in its entirety.  
         [0038]     The invention can be used with multi-ink metameric codes for optimal information storage. Metamerism is the property where two objects with different spectra produce in the same visual effect. The human-visual system (HVS) sees color through a set of three filters. Any images whose spectra produce the same three signals through these three filters produce the same signal in the HVS. The spectrum of an image depends on the illuminating spectrum. Reflection spectra that are metameric under one lighting source can be distinguished under a different lighting source. Therefore, metamerism should be referred to a particular illumination. An example is black pigment ink and black dye-based ink. The dye-based ink generally has higher reflectance in the red and infrared. In the following, metameric inks refers to two or more inks that appear the same under normal daylight or room illumination. Inks can also differ in their luminescent spectrum. The term luminescence includes phosphorescence and fluorescence. The definition of a metameric ink used herein includes inks that can have different characteristics under certain conditions versus the ink&#39;s color under normal lighting. An example is black fluorescent ink.  
         [0039]     Encoding in a metameric image can be, for example, used in a multi-level barcode encoding scheme. A metameric encoded image hides information using a set of metameric inks. The metamerism can be detected using a set of sensors with different spectral characteristics that respond differently to the different metameric inks. There is a range of possible encoding schemes. A naive scheme simply uses two (or N) metameric inks and encodes information using any standard two-level (or N-level) barcode such as PostNet, DataMatrix or PDF417. In the two-level case, one ink is used for the normally black portions and a second metameric ink is used for the normally white areas. In the N-level case, ink n is used to encode level n, where n ε {1,2 . . . N}.  
         [0040]     A more sophisticated approach would encode information in linear combinations of multiple metameric inks. Consider an image with N metameric inks. There is a relationship f(σ 1 , σ 2 , . . . σ N )=c describing the combinations of densities of inks that produce the same visual effect, where σ 1  is the surface density of ink i. In a simple case this relationship is approximately linear, with a vector of weights w i  so that the metameric combinations satisfy Σ i w i σ i =c. The weights and surface densities are all positive. Information can be encoded in an image in the combination of σ 1 &#39;s used to reach c.  
         [0041]     It is desirable to allow c to be a predetermined function c(x, y) of position in the image, so that the image as seen in the HVS is recognizable. Define s i (x, y)=w i σ 1 (x, y)/c(x, y). The set s 1 (x, y) defines a direction independent of c(x, y) in the space spanned by the metameric inks at each point in the image. The sum over the inks satisfies Σ i s i =1. The naive encoding scheme represents each level by a different ink, that is, simply set S n =1 for the n that corresponds to the encoded information level, and s j =0 for the n≠j. A more complex and higher density encoding can be achieved for two inks by selecting the value s 1  in {0, 1/M, 2/M . . . (M−1)/M, 1} and setting S 2 =1−s 1 . Now M values can be encoded. For more than two inks, the number of combinations can be increased. For example with three inks and M=3 there are nine combinations of the three s&#39;s: (1 0 0) and two permutations, and (⅔, ⅓, 0) and 5 permutations. For 4 metameric inks and M=3 there are 20 combinations so each position can encode over 4 bits. The data can be arranged in a pattern like a barcode.  
         [0042]     Continuous watermark encoding can be provided. The phase space watermark is an example of a quasi-continuous grayscale watermark created by adding a linear combination of wavepackets based on some data to an image. A disadvantage of the phase space watermark is that when the image is examined closely, the wavy noise can be seen. The watermark tends to degrade the image quality. Employing two metameric inks allows an improved watermark. Represent the image c(x, y)=c(x, y)·(s 1 (x, y)+s 2 (x, y)). If the watermark is δ(x, y) then set s 1 (x, y)=0.5+δ(x, y) and s 2 (x, y)=0.5−δ(x, y). The HVS sees c(x, y), while a detector designed to see the difference between ink  1  and ink  2  sees a signal proportional to δ(x, y).  
         [0043]     Referring also to  FIG. 7 , one example of a system  40  for reading the printed indicium or document  12  is shown.  FIG. 7  shows a system diagram which includes visible and excitation light sources  42 ,  44 , image capture devices (in this example, they are scanners)  46 ,  48 , storage  50 ,  52  for multiple images (may be more then two if more then two types of encoding are used) and a processing computer  54 ,  56  which includes its own memory, software program, algorithms, parameters and interfaces to external systems. The system in  FIG. 7  is used to read and decode the information embedded in the document  12 . That information can then be passed to another computer system to apply the cryptographic, algorithms and/or the integrity algorithms. In an alternate embodiment, this could be done in the same computer. The document can be scanned under a excitation source, such as UV light  44  or any other suitable excitation source. The resulting image can be converted to text using standard Optical Character Recognition (OCR) methods.  
         [0044]     The text is parsed to identify all letters or characters printed with BFI. A binary file is created by assigning a “0” to each non-BFI letter and a “1” to each BFI letter. The resulting binary information will be referred to as “AIR data”. The text and the AIR data are used together to verify/calculate digital signatures or integrity such as by using known numerical methods.  
         [0045]     In an alternate embodiment of the present invention, additional information can be encoded using multiple different types of fluorescent or luminescent inks responding to different wavelengths, such as the UV spectrum. Using this method, the density of data that can be encoded can be significantly increased. As such, spectral resolution of the detection system can be enhanced for applications that require higher data density.  
         [0046]     The BFI presence can be detected by a simple fluorescence detector for a broad signal; such as 70-80 nm bandwidths for example. Additional information can be encoded using variations of BFI which have unique properties such as phosphorescence, specific narrow emission wavelength of emission, IR absorbance, etc. By using these combinations a user can encode more information that can be read by using different detectors which are respectively sensitive to the unique characteristic. Examples of such characteristics include special signature inks.  
         [0047]     An illustration of an ink with a phosphorescent taggant provided by a rare earth complex is shown in  FIG. 6 . This ink can be identified also with a detector that has special filters for narrow width fluorescence detection (such as 5-10 nm for example) which will differentiate it from a broad band detector. In this embodiment, the difference in fluorescence detection can be obtained by measuring the emission at two different wavelengths: 598 nm for the broad band detector and 616 nm for the narrow band detector.  
         [0048]      FIGS. 8-10  show one example of use of the present invention in a document. In this example the document is a U.S. tax W-2 form that uses features of the present invention to add authentication and integrity to the printed information.  FIG. 8  shows the image  58  of the W-2 form captured with a conventional camera using normal lighting conditions, as it is seen by the human eye. For example, this could be by use of visible light source  42  and reflected image scanner  46  shown in  FIG. 7 .  
         [0049]      FIG. 9  shows the negative image  60  of the same W-2 form captured with a UV camera with the document exposed to UV light. For example, this could be by use of UV light source  44  and fluorescent image scanner  46  shown in  FIG. 7 . This image shows the areas (letters, numbers and marks, e.g. lines) that were printed with BFI.  
         [0050]      FIG. 10  illustrates the result  62  of processing the images from  FIGS. 8 and 9 . The text box  64  in the lower right area of the form has encoded information using an algorithm that assigns a binary value of “1” (one) to any letter printed with the special second ink (BFI in this example) and a value of “0” (zero) to all other letters. Punctuation and spaces are not given values. The result of such encoding is a string of digital bits that can be used for message authentication, digital signatures and/or integrity.  
         [0051]     The processing of images from  FIG. 8  and  9  can rely on correct alignment of the two images. There are a variety of methods to achieve alignment, including the printing of specific marks (crosses, circles, lines) that are visible on both images and coincide or have a known spatial relationship. In this example the lines around the document (border) are used to ensure alignment of the two images. Reference is made to U.S. patent application Ser. No. 10/128,113 which is hereby incorporated by reference in its entirety. Use of known spatial relationships can use one ink and two detectors. The invention can use more than one ink and multiple detectors; or perhaps only one detector with multiple detection capabilities. The detector(s) can be used to establish spatial relationships between/among the characters/symbols printed with different respective inks. This can be understood best with reference to  FIG. 5A . When reading the second information stored with the second ink (line  22 ) spaces between the characters of line  22  can be actual real spaces in the line  20  and/or the characters/symbols printed with the first ink shown in  FIG. 24 .  
         [0052]     The information shown in  FIG. 10 , in the lower right box  64  can be used for authentication and integrity of the document through known methods such as MAC (Message Authentication Code), digital signatures, error correction codes (for example Reed-Solomon). The numbers in  FIG. 10  are representative, not actual calculated values. This system and method can be used for any type of printed document.  
         [0053]     In some cases, it is desirable to have the authentication, integrity and/or redundancy capabilities offered by the additional codes described above without making their presence obvious to the casual observer. In other cases, space is at a premium. Hence the capability of applying these codes without taking additional space on the printed area is a definite advantage. Similarly, machine printed and/or machine readable documents can be enhanced using this invention. An example of such applications are proof of payment barcodes applied by postage meters that can use this invention to apply digital signature and redundancy codes. Applying these codes using the method described in this invention does not need to use additional printing area. Additionally, this can be an additional defense against fraudulent copy of the document, as it requires specialized equipment and knowledge.  
         [0054]     The present invention can provide a system and method for adding inconspicuous authentication and integrity to printed documents. The present invention can solve the problem of the prior art by adding the codes necessary for authentication, integrity and/or redundancy using a printing method which is not visible under normal conditions and does not interfere with the appearance of the document. An example of such a method is using black fluorescent ink (BFI) to print selected characters of a document. The information used for the digital signature and (or) redundancy purposes is encoded by printing selected characters with a special ink and printing the rest of the document with normal ink.  
         [0055]     To the casual observer who examines the document under normal lighting conditions, the document has no additional visible information. When the document is examined under appropriate UV light, selected characters will change color. Their position in the text can be decoded and converted into numbers. These numbers can be used to add digital signatures and/or redundancy to the document. The present invention can be used in various applications including, but not limited to, postage meters, Digital file room (DFR) concept, Database Management Systems (DBMS) document management applications, and document encoding systems. This invention provides a method to add information necessary for authentication and integrity without creating additional visible codes on printed documents and without using additional printing area. This invention describes a method of adding digital signatures and error correction codes to printed documents without altering the appearance of the original document. This invention provides authentication, integrity and redundancy for printed documents without adding any visible artifacts and without using any additional printing area.  
         [0056]     It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.