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watermark) can be used later to trace data to its creator, to prove authorship or rights to the material, or to use as a proof of purchase. Digital watermarks can achieve these goals because invisible marks can be embedded securely and robustly; that is, such watermarks can be retrieved only with an owner’s secret key and can survive many common attacks. Although copyright protection is the original motivation for developing digital watermarks, the technology has found a multitude of potential applications not anticipated by the pioneers in the field. Awareness of the technology and knowledge of its use in application domains other than copyright protection deserves a wider audience. When a watermark holds executable content, the marked document can perform actions and operations and interact with the application environment. Thus, a multimedia document, as well as other kinds of documents, becomes an …