Digital watermarking refers to the practice of embedding specific visible or invisible information into a digital signal or multimedia product such as a video, image, graphic or audio file. The idea behind digital watermarking is to deter others from changing the file, and copying or using it in an unauthorised manner. Watermarking was first used in 1282 when specific paper had watermarks embedded. With visible digital watermarking, the information is fairly easy to distinguish in the image or video. It can be the name of the company and a copyright notice as well as a warning not to copy. The watermark is normally part of the picture and can include an application which makes it possible to identify any attempt to distort or remove the digital watermark from the video or image. It can also be invisible where the user cannot easily detect the inclusion of the information that is hidden in the medium.
In essence then, digital watermarking hides information to ensure that a party can show ownership if the work is spotted somewhere else where it has been used without proper authorisation to do so. It is also used to prevent unauthorised copying and usage of digital products. Digital watermarking is often used in broadcast monitoring, source tracking, and secret communication, in addition to copyright protection on the Internet.
Digital watermarking has certain characteristics including the ability to show ownership, prevention of the removal of the digital watermarks from the multimedia, permanency ensuring that even after several steps to remove the marks, that the marks should still be visible, and detection which is an algorithm to detect any attempts to remove the marks. Where the digital mark is visible, it is called a robust mark and where it is not easily visible it is called imperceptible.