Watermark fonts
First Claim
1. A method of embedding a digital watermark in a text document having text characters represented as character codes, the method comprising:
- providing a digital message comprising message symbols;
providing a watermarking font representing text characters with sets of alternative image character representations, where the alternative image character representations correspond to different message symbols and appear similar to a viewer but are distinguishable by an automatic reader;
to hide a message symbol from the digital message in one or more text characters of the text document, selecting a predetermined image character representation of the one or more text characters corresponding to the message symbol to be hidden in the one or more text characters; and
inserting the predetermined image character representation into the text document.
1 Assignment
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Accused Products
Abstract
A method of embedding and detecting a digital watermark in a rendered document, such as printed or displayed document, by using a watermark font. The watermark font has multiple representations of each character, wherein each character representation is visibly similar but the difference can be detected in the rendered version of the font by a computer. This watermarking system can efficiently be used to identify and forensically track all rendered, especially printed, documents. In fact, if each character is represented twice, the system can use standard ANSI characters between character codes 0 and 127, and a slightly modified version of each of these characters represented with character codes 128 to 255, such that each version of a character carries a bit. For this example, the watermark embedding process is as simple as whether or not to add 128 to the standard ANSI code. Furthermore, if the character codes are modified before the file is saved, the character codes carry the watermark within the electronic file, as well as the rendered characters carry the watermark in the rendered version.
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Citations
24 Claims
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1. A method of embedding a digital watermark in a text document having text characters represented as character codes, the method comprising:
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providing a digital message comprising message symbols;
providing a watermarking font representing text characters with sets of alternative image character representations, where the alternative image character representations correspond to different message symbols and appear similar to a viewer but are distinguishable by an automatic reader;
to hide a message symbol from the digital message in one or more text characters of the text document, selecting a predetermined image character representation of the one or more text characters corresponding to the message symbol to be hidden in the one or more text characters; and
inserting the predetermined image character representation into the text document. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method of automatically reading a digital watermark from text characters in a rasterized version of a text document, the method comprising:
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performing character recognition on the text characters in the rasterized version to determine font size and line orientation of the text characters in the text document; and
comparing image representations of the text characters to at least one preset character representation in a watermarking font for similarity to extract one or more auxiliary data symbols in a digital watermark message hidden in the text document. - View Dependent Claims (18)
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19. A method of creating a digital watermark font comprising:
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providing text characters; and
providing a set of at least two image representations for the text characters in the set, wherein the at least two image representations correspond to different data symbols and appear substantially similar to a viewer, yet are distinguishable by an automated reader. - View Dependent Claims (20)
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21. A method of reading a digital watermark embedded in a text document, the method comprising:
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receiving image representations of text characters in an image representation of a text document;
for text characters in the text document, identifying which one of a set of alternative image representations of the text character in a watermarking font corresponds to the received image representation; and
extracting a sequence of message symbols embedded in the text document by finding message symbols corresponding to the identified image representation, wherein the alternative image representations for a text character appear substantially similar to a viewer but are distinguishable by an automatic reader, and correspond different message symbols. - View Dependent Claims (22, 23, 24)
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Specification