Background

The idea of hiding data within computer images is not new. Multiple programs already exist for this purpose, and some are available for download on the Internet. These programs, such as JPHIDE[2] and GZSteg[5] take images in common file formats like JPEG and modify them slightly to include a user-specified text message. Each has its limitations, and other programs have been created to detect images that have been processed by the steganography programs[3]. For example, steganography with JPEG images is more noticeable, due to the lossy compression algorithm JPEG uses. In the compression, the raw image is changed and muddied significantly, and the difference between the original and the modified image is magnified. The change may also effect a difference inthe disk space each image occupies. The algorithm chosen also affects the detectability of the steganography. If an algorithm that hides large amounts of information is used, there will be a much greater change in the image's appearance. Therein lies the challenge and trade-off of steganography: hide the most data with the least noticeable (to both humans and computers) change in the image.