A watermark is information embedded within a file. In the most common usage, watermarks are added to images to identify the image's creator.
Digital watermarks may be used to verify the authenticity or integrity of the carrier signal or to show the identity of its owners. It is prominently used for tracing copyright infringements and for banknote authentication.
Like traditional watermarks, digital watermarks are only perceptible under certain conditions, i.e. after using some algorithm, and imperceptible anytime else.
In contrast to a digital-signature, watermarks can typically easily be added by a third party. A watermark can be forged, but should typically be hard to remove.
