A gradient image dependent fragile watermarking for improved security and localization

Most fragile watermarking techniques are block-wise independent based schemes. They are either vulnerable to vector quantization (VQ) attack or sacrifice localization accuracy to improve security. This paper presents a gradient image dependent fragile watermarking scheme, which thwarts VQ attack while providing superior localization properties. The proposed technique provides distinct input keys for each image block from a large (1024! - 8770-bits entries) key space, a master key, a session key and block-wise permutated versions of a gradient image. The watermarking scheme requires only the master key (one time exchange) and the session key (each session) to be exchanged between the communication parties securely. Analysis and experimental results indicate that the proposed method possess better authentication and tamper detection capabilities compared to many other fragile watermarking schemes available in the literature. It can also be seen that the proposed scheme is suitable for both digital images and video.