digital watermark

A pattern of bits embedded into a file used to identify the source of illegal copies. For example, if a digital watermark is placed into a master copy of an audio CD or a DVD movie, then all copies of that disc are uniquely identified. If a licensee were to manufacture and distribute them in areas outside of its authorized territory, the watermark provides a trace.

The watermark developer has to find creative ways of altering the file without disturbing it for the user. It is extremely difficult to embed a watermark within an ASCII file, which is just raw text. But it is relatively easy to alter a few bits within audio, video and graphics formats without making a noticeable difference on playback or display.