Watermarks provide a cheap means of identifying copyrighted works and notifying the would-be users how to contact the copyright owner to gain permission for use. Spread-spectrum watermarking and steganography are the most common forms of digital watermarking today. Steganography encodes hidden digital sequences within the binary file of the copyrighted work. The encoded watermark is often referred to as a work's digital signature. Although the watermark is embedded digitally within the image, it remains part of the image even when printed into hard copy, and can be read later by scanning the image into a computer.
Watermarks even survive the telefax process.
An intelligent fingerprint is a tell-tale script of the violator's location and uses of the copyrighted work. To enforce copyright protection, the owner simply follows the fingerprint trail. Accordingly, when a publisher first commits his or her work to a digital format such as scanning it or creating a CD-ROM, the watermark and fingerprint codes are integrated into the image from the outset. This enables intelligent enforcers to locate the wrongdoer who first posted the copyrighted material, even if posted anonymously on vast public databases like the Usenet. As mentioned in that article, the court in the case of Religious Technology Center v. Netcom held that Netcom, an ISP, was not liable for copyright infringement when it was unaware that its users were engaged in downloading copyrighted materials.