A Novel Semi-fragile Digital Watermarking Scheme for Scrambled Image Authentication and Restoration

More than ever, the practical and accurate watermarking technologies are called for the growing amount of exchanged digital image over the Internet. To protect the integrity and authenticity of digital image and to enhance the effect of tamper detection and restoration, we design and implement a semi-fragile watermark based on cat transformation, mostly used to locate tamper and recover for the transformed image and plain-image. The watermark which consists of two parts: the authentication watermark and recovery watermark, is embedded into the 2 least significant bit (LSB) of the pixel of the original image. The authentication watermark is calculated by the pixel value comparison and the parity check code, while the recovery watermark contains the average pixel value of the Torus image block. In the detection side, we use the hierarchy concept to locate the tamper in three layers and recover the attacked image in two layers. By using the hierarchy concept, this algorithm has another superiority that tamper can be detected on confused image. The experimental results show that our algorithm can accurately locate tamper and realize the content recovery and effectively prevent the vector quantization attack. Compared with other algorithms, this algorithm has better effect of tamper location and recovery.