A watermark is identifiable code of some sort embedded into the data making up an image, sound, recording, video, software program, or other material. Normally a watermark is designed not to be obvious and not to interfere in any way with the usefulness of the information containing it, though this is not always the case.
Watermarking has taken on a new importance in the digital era. Still images, video, music, text, and software are all easily copied and illegally distributed, causing the authors to lose out on considerable income in royalties. By embedding identifying information in a file, watermarking software enables authors to control the distribution of and to verify ownership of their digital information. It essentially “copyrights” digital information. Various methods exist, but many consist of very short (2-5 microseconds long) pieces of code containing all the relevant data about the copyright owner and performance royalties.