The adjective digital refers to something such as text or images that is stored electronically, in contrast to text or data that is in concrete form on, for example, a piece of paper. A watermark, in the world of publishing, refers to a translucent mark incorporated into paper to identify the manufacturer and/or as a mark of authenticity and to discourage counterfeiters, in the case of currency. Digital watermarking is the incorporation of an analogous mark on digital files. It is related to and used for the same purposes as steganography, the science of hiding information.
Digital watermarking may be either visible or invisible. At first, it might seem that invisible digital watermarking could be useless, but in fact, this type of watermarking is usually designed so that it is invisible only on the website in which it was embedded and becomes visible if the material is transferred, copied, or pasted to another place. Such a digital watermark can be overlooked by the thieves or plagiarists, but serve to expose them. Visible watermarking, on the other hand, can serve to deter theft in the first place.
Another use of visible digital watermarking is in demo versions of software applications. While some demos limit use by turning off features or granting a license for a limited length of time, often 30 days, others allow full use of features indefinitely, but place a digital watermark on every saved or exported file, so that these files cannot readily be used or shared in any commercial venue. This encourages users to purchase a working copy of the software.
A third use of digital watermarking is in tracking of distribution of a digital file. This can be done in the spirit of sending out a message in a bottle and seeing where a file ends up, how many times it’s picked up, and how it is used. Alternatively, it can be used to track an illegal distribution route.
Software products are available to assist in digital watermarking. These products assist in the creation and editing of digital watermarks. The watermarks can be based on an image — such as a logo, a text copyright notice, a website URL, or simply the word SAMPLE for images that are used for demonstration purposes. Digital watermarking software has features such as filters to add effects to watermarks, batch processing, and adjusting the image format for greater security. Digital watermarking software can either be a standalone software application or it can be an add-on to an existing program to extend its functionality.