Digital watermarking provides new ways of authenticating digital media

Digital watermarking is an emerging concept, but don't let the name fool you. It's not used for authenticating documents. (That's the job of digital signatures.) Unlike a paper watermark, a digital watermark plays off that other sense of the word. It refers to the ability to unobtrusively include information in a file, and is commonly executed through a variety of cryptographic techniques, collectively known as "steganography." But instead of gently rearranging the paper fibers, digital watermarks gently rearrange bits scattered through a piece of digital content.