In a few words, the concept of steganography is to conceal messages inside other messages in a way that the concealed messages are undetectable by others. There are many methods to accomplish this messaging concealment. Among these methods are digital signatures, watermarks, and invisible inks. A digital watermark is a image, digital signal or pattern that is embedded permanently into another image. Digital watermarks are utilized for the protection of ownership rights for audio, image, text and video products.
Digital watermarks can serve as digital signature for subsequent copies.
There are two types of watermarks, visible and invisible. Normally, visible watermarks are used as logos to display property ownership. They are minimally intrusive on the primary image but still recognizable. Invisible watermarks are images that cannot be seen but can be detected by special algorithms. Invisible watermarks are used to identify the source of the document such as author, owner, etc.