METHODS AND SYTEMS USING MULTIPLE WATERMARKS

Two or more digital watermarks, with different characteristics, are embedded in a document. The characteristics are chosen so that the watermarks will be affected in different manners if the document is subsequently copied or reproduced. The detection process or mechanism reads two or more of the watermarks and compares their characteristics. While wear and handling may change the characteristics of the digital watermarks in a document, the relationship between the characteristics of the multiple digital watermarks in a document will nevertheless give an indication as to whether a document is an original or a copy of an original. Document wear can be independently assessed and used as an aid in interpreting the detected watermark characteristics.