A forensic watermark, also called a digital watermark, is a sequence of characters or code embedded in a digital document, image, video or computer program to uniquely identify its originator and authorized user. Forensic watermarks can be repeated at random locations within the content to make them difficult to detect and remove.
Forensic, in a general sense, means "related to...(WhatIs.com)
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The main purpose of forensic watermarking is to protect the interests of content creators against illegal use and distribution of copyrighted digital works. While forensic watermarks cannot prevent such activity altogether, they can make it easier for copyright holders to detect it and to identify people who engage in it. A forensic watermark can alert honest users when they have received illegitimate documents or programs.
The main limitation of forensic watermarking technology is the occasional occurrence of false positives, in which legal copies of a document, image, video or program are tagged as unauthorized. This can happen when a used computer is traded and re-registered in the new user's name. It can also occur in certain cases when content becomes unintentionally corrupted or certain critical files are removed by hard disk cleanup or anti- spyware utilities.
Forensic watermarks have gained acceptance in the software and digital video industries. Other applications in which the technology hold promise include digital music and electronic books (e-books).