Digital watermark

A digital watermark is a small, almost unnoticeable alteration to a digital work like an image, a photograph, or a sequence of sounds. The watermark cannot be perceived with the human eye, but can be detected with a computer program designed for the purpose.

Digital watermarks can be used to embed identifying information into the digital work. Moreover, software that works with images can automatically detect the hidden markings and act accordingly: not permit copying, for example. If the watermark contains a serial number, any given copy of a watermarked work can be logged and recorded somewhere, allowing the author to track down the source of unauthorized copies.