A Multi-Purpose Semi-Fragile Watermarking Scheme for Digital Images

Digital images can be easily shared via Internet and conveniently processed for queries in databases. Internet carries a large variety of images, which can tolerate minor changes. In general, minor data alterations may be acceptable if they still maintain the perceptual quality of the signal. For all-out forgeries, substantial modification of the content and other malicious attacks can be identified and rejected. So a “soft” image authenticator is desired for the Internet. Data hiding adds perceptually irrelevant information in order to embed data, while compression removes this irrelevancy and redundancy to reduce storage requirements. There exists a duality between data hiding and compression. A semi-fragile watermarking scheme has been proposed in this paper for the compression and authentication of digital images. The watermark consists of an authenticator watermark for authentication and tamper assessment for a given image, and chrominance watermark for “piggy-backing” colour components into the luminance component. The multipurpose watermark is designed by exploiting the orthogonality of various domains (DCT and DWT) used for authentication, colour decomposition and watermark insertion.