One of the hallmarks of the Web is that information providers and consumers can be connected easily and effortlessly. Information providers post their products on their servers and interested consumers seek them out. If your goal is to reach a general audience, then restricting or controlling access is not an option. Digital watermarking is a method that supports an open access environment. Conventional watermarks are ingrained in the paper as proof of ownership and authenticity.
Watermarks are typically imperceptible unless the page is viewed against a source of light.
A digital watermark is similar. Images are modified to contain embedded information that serves to authenticate the source of the image. Some digital watermarks are visible, though not obtrusively. IBM , for example, has developed a watermarking system that was first applied at the Vatican Library in Rome. Priceless documents in the collection are scanned and marked with the Vatican seal.