Watermark fonts

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.

Dependencies are inferred from the claim text.