Marking images of text with speckle patterns for theft deterrence

Abstract

The present invention provides methods and apparatus for embedding an identifying pattern of visible speckles into the digitized image of each page of a document. A speckle is a cluster of black or white pixels. Speckles are printed as black speckles on the white paper, or conversely, as areas of missing black removed from the black text characters, called white speckles. The collective pattern of all embedded black and white speckles on a single document page is called a specklemark. A specklemark can survive contrast manipulations on photocopiers and binary rasterization done by fax scanning prior to data transmission. The random pattern of the black and white speckles visible in the digitized image of a document page can be detected automatically, and by systematically matching the detected pattern with those known to have been embedded into marked copies of a document page, a specific document copy can be identified. Methods for composing, embedding and detecting specklemarks are the subject of this patent.

1 . A method of enhancing document security and detecting fraud, comprising: 
 embedding information into an original document and subsequently determining the presence of the embedded information in a copy of the original document, the embedding step including:    providing a digitized image having at least one image plane, the at least one image plane being represented by an image array having brightness data for a plurality of pixels, each of said pixels having at least one color component and a pixel position;    computing a first set of candidate positions for embedding speckles into the digitized image based on information to be embedded;    computing a second set of candidate positions for embedding ghost speckles into the digitized image based on the information to be embedded; and    embedding the speckles into the digitized image to create a composite image.    
   
   
       2 . A method comprising: 
 embedding information into at least one page of a document copy and subsequently detecting whether said information had been embedded into at least one page of a suspect document copy,    said document copy being in a rasterized format, herein called a digitized page image,    said information being embedded through steps of: 
 providing the digitized page image having at least one image plane, each said image plane being represented by an image array having brightness data for a plurality of pixels, each of said pixels having at least one color component and having a pixel position;  
 computing a first set of candidate positions for embedding black speckles into the page image based on said information to be embedded;  
 computing a second set of candidate positions for embedding ghost speckles into the page image based on said information to be embedded; and  
 embedding black speckles into the page image at positions where they are not near the edges of the page image's text.  
   
   
   
       3 . The method of  claim 2 , said other information being embedded into said at least one page of a document copy and subsequently detecting whether said other information had been embedded into at least one page of a suspect document copy, said other information being embedded through steps of: 
 computing a third set of candidate positions for embedding white speckles into the page image based on said information to be embedded; and    embedding white speckles into the page image at positions where they are predominantly or totally within the edges of the page image's text.    
   
   
       4 . The method of  claim 3 , a printed copy of said suspect document copy being converted into a rasterized format by scanning said printed copy forming a digitized suspect page image.  
   
   
       5 . The method of  claim 2 , the subsequent detection of said information in a suspect page of a document copy being accomplished through steps of: 
 providing a digitized suspect page image having at least one image plane, each said image plane being represented by an image array having brightness data for a plurality of pixels, each of said pixels having at least one color component and having a pixel position;    recomputing the first set of candidate positions for embedding speckles into the page image based on said information to be embedded;    recomputing the second set of candidate positions for embedding ghost speckles into the page image based on said information to be embedded;    geometrically aligning said suspect page image with the page image;    determining at each black speckle position whether the suspect page image had a nearby black speckle;    computing the number of black speckle positions for which that suspect page image had a black speckle nearby;    determining at each ghost speckle position whether the suspect page image had a nearby black speckle;    computing the number of ghost speckle positions for which that suspect page image had a black speckle nearby; and    determining whether the suspect printed page possessed said information to be embedded.    
   
   
       6 . The method of  claim 5 , the determining whether the suspect printed page possessed said information to be embedded being based on the number of black speckle positions, the number of black speckle positions for which the suspect page had a nearby black speckle, the number of ghost-speckle positions, and the number of ghost-speckle positions for which the suspect page had a nearby black speckle.  
   
   
       7 . The method of  claim 5 , the subsequent detection of said other information in a suspect page of a document copy being accomplished through the additional steps of: 
 recomputing the third set of candidate positions for embedding white speckles into the page image based on said information to be embedded;    determining at each white speckle position whether the suspect page image had a nearby white speckle;    computing the number of white speckle positions for which that suspect page image had a white speckle nearby; and    determining whether the suspect printed page possessed said other information to be embedded based on: 
 the number of white speckle positions, and  
 the number of white speckle positions for which the suspect page had a nearby white speckle.  
   
   
   
       8 . A system for enhancing document security and detecting fraud, comprising: 
 a system for embedding information into an original document and subsequently determining the presence of the embedded information in a copy of the original document;    a system for computing a first set of candidate positions for embedding speckles into a digitized image based on information to be embedded, and for computing a second set of candidate positions for embedding ghost speckles into the digitized image based on the information to be embedded, the digitized image having at least one image plane, the at least one image plane being represented by an image array having brightness data for a plurality of pixels, each of said pixels having at least one color component and a pixel position; and    a system for embedding the speckles into the digitized image to create a composite image.    
   
   
       9 . The system of  claim 8 , further comprising: 
 a system for recomputing the first set of candidate positions for embedding speckles into the page image based on said information to be embedded, and for recomputing the second set of candidate positions for embedding ghost speckles into the page image based on said information to be embedded;    a system for geometrically aligning said suspect page image with the page image;    a system for determining at each black speckle position whether the suspect page image had a nearby black speckle;    a system for computing the number of black speckle positions for which that suspect page image had a black speckle nearby;    a system for determining at each ghost speckle position whether the suspect page image had a nearby black speckle;    a system for computing the number of ghost speckle positions for which that suspect page image had a black speckle nearby; and    a system for determining whether the suspect printed page possessed said information to be embedded.    
   
   
       10 . The system of  claim 8 , the system for determining whether the suspected printed page possessed said information to be embedded making the determination based on the number of black speckle positions, the number of black speckle positions for which the suspect page had a nearby black speckle, the number of ghost-speckle positions, and the number of ghost-speckle positions for which the suspect page had a nearby black speckle.  
   
   
       11 . The system of  claim 8 , the subsequent detection of said other information in a suspect page of a document copy being accomplished through the additional systems of: 
 a system for recomputing a third set of candidate positions for embedding white speckles into the page image based on said information to be embedded;    a system for determining at each white speckle position whether the suspect page image had a nearby white speckle;    a system for computing the number of white speckle positions for which that suspect page image had a white speckle nearby; and    a system for determining whether the suspect printed page possessed said other information to be embedded based on: 
 the number of white speckle positions, and  
 the number of white speckle positions for which the suspect page had a nearby white speckle.  
   
   
   
       12 . A program product stored on a computer useable medium for enhancing document security and detecting fraud, the computer useable medium comprising program code for causing a computer system to perform the following steps: 
 embedding information into an original document and subsequently determining the presence of the embedded information in a copy of the original document;    computing a first set of candidate positions for embedding speckles into a digitized image based on information to be embedded, and for computing a second set of candidate positions for embedding ghost speckles into the digitized image based on the information to be embedded, the digitized image having at least one image plane, the at least one image plane being represented by an image array having brightness data for a plurality of pixels, each of said pixels having at least one color component and a pixel position; and    embedding the speckles into the digitized image to create a composite image.    
   
   
       13 . The program product of  claim 12 , the computer useable medium further comprising program code to cause the computer system to perform the following additional steps: 
 recomputing the first set of candidate positions for embedding speckles into the page image based on said information to be embedded, and for recomputing the second set of candidate positions for embedding ghost speckles into the page image based on said information to be embedded;    geometrically aligning said suspect page image with the page image;    determining at each black speckle position whether the suspect page image had a nearby black speckle;    computing the number of black speckle positions for which that suspect page image had a black speckle nearby;    determining at each ghost speckle position whether the suspect page image had a nearby black speckle;    computing the number of ghost speckle positions for which that suspect page image had a black speckle nearby; and    a system for determining whether the suspect printed page possessed said information to be embedded.    
   
   
       14 . The program product of  claim 13 , the determination of whether the suspected printed page possessed said information to be embedded being based on the number of black speckle positions, the number of black speckle positions for which the suspect page had a nearby black speckle, the number of ghost-speckle positions, and the number of ghost-speckle positions for which the suspect page had a nearby black speckle.