Watermarking method and apparatus
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United States of America Patent
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Jul 14, 2009
Grant Date -
Jul 26, 2007
app pub date -
Apr 4, 2003
filing date -
Apr 4, 2003
priority date (Note) -
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Abstract
The invention provides a method and apparatus for watermarking a document, the method comprising: associating the document with an identification number; generating (70) a first set of numbers using a seed for the number generation comprising or derived from the identification number; applying a transform (62) to at least a portion of an image of the document to form a transform of the image; defining a second set of numbers comprising transform coefficients from the transform of the image; forming a modified second set of numbers based on the first set and the second set; substituting the modified second set for the second set in the transform of the image to form a modified transform (72); and applying an inverse (74) of the transform to the modified transform to thereby produce a modified image of the document; whereby the modified image of the document or an output of the modified image constitutes the watermarked document.
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