The Second Boston University Student Conference on Information Assurance and Cyber Security, Boston, MA (December, 2006)
In today’s technology centric society there is a compelling need to embed information in various digital media for many reasons, both noble and nefarious. One technique that has been becoming increasingly popular is watermarking. Watermarking involves embedding information into digital images, videos, or audio files. These watermarks can be hidden from the user or glaringly obvious, and their purpose may anything from uniquely identifying what camera was used to capture an image to transmitting covert messages. This paper focuses on single images, although much of what is discussed can be readily applied to audio and video sequences as well.
The information that is embedded as part of a digital watermark can be almost anything. It might be the digital equivalent of a traditional paper watermark where the watermark is another image in itself, such as a personal check, a dollar bill, or the author’s signature on a famous work of art. In these cases the watermark is easily visible to the user. A digital watermark, however, is most often hidden and might contain any sequence of bytes such as ASCII text, a binary data file, or a hidden encryption key.
This paper describes digital watermarks in more detail. The types of watermarks are presented, followed by some of the applications they are used in and the reasons that watermarks are created and distributed in images. The metrics used to determine the robustness of watermarking techniques are then described, followed by a summary of the methods used to discover the presence of hidden watermarks. Four sample methods are then briefly described to demonstrate some of the current techniques used to create and decode watermarked images. Finally, a synopsis of the author’s implementation of the least significant bit (LSB) algorithm initially proposed by Van Schyndel, Tirkel, and Osborne (1994) is presented.
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