On October 9, 2003, a redesigned version of the $20 bill went into circulation in the U.S. Among other features, the bill includes watermarks that can be used to verify its authenticity. Traditional watermarking techniques are intended to prevent duplication, and digital watermarks have a similar purpose. They can be embedded into virtually any digital media, including images, audio and video, and even program code. Digital watermarks are usually imperceptible to humans and are designed to be read by a computer to communicate information such as copyright ownership and legal uses of the watermarked media.
The first site (1) contains two articles about the new $20 bill: one from a government news release and one from the U.S. Bureau of Engraving and Printing. Each article gives some facts about U.S. currency in general and the security features integrated into the redesigned bill. The Money Factory (2) has a section devoted to anti-counterfeiting techniques used in the making of money. The easily overlooked links at the right side of the page explore topics such as Advanced Copier & Printer Technology and the history of the security printer used by the U.S. government. Moving on to digital watermarking, a good introduction to the subject can be found here (3). The site explains the purpose and applications of digital watermarking. A separate section provides information about the Certimark project, which is developing a benchmark to evaluate characteristics of watermarks. Watermarking World (4) is a hub for information related to digital watermarking. Besides maintaining a frequently asked questions list and links to industry and academic research, the site serves as an online forum for the watermarking community. An algorithm used to embed watermarks in audio tracks is evaluated in this paper (5). The authors experimented with different parameters of the algorithm to achieve a balance between sound quality and watermark robustness. Another interesting research paper considers how to maintain a digital watermark on electronic documents when they are printed and re-scanned (6). Since no digital information can be transferred from an electronic document to a hard copy, the watermark clearly must be visible on the page. However, a certain degree of loss is inherent in the scanning process, and the authors propose a method of dealing with this information loss and recognizing visible watermarks for re-integration into the electronic version. The April 2003 issue of the IEEE Transactions on Signal Processing includes this paper on hardware implementation of digital video watermarking (7). This is a unique approach since most watermarking algorithms are realized in software, but a wholly hardware implementation has the advantage of being smaller and having lower power consumption due to its dedicated functionality. The Information Hiding Homepage (8) has a good collection of resources related to digital watermarking, fingerprinting, and other forms of steganography (the technical term for information hiding). Two examples of image downgrading are given, as well as insights into MP3 steganography. [CL]