A reversible two-level image authentication scheme based on chaotic fragile watermark

For image authentication, the capability of accurately locating tampered pixel and ensuring security is desirable. In this paper, we propose a novel reversible two-level image authentication scheme based on chaotic fragile watermark. In the embedding process, at the pixel level, by utilizing the pixel correlation technology, the location watermark of each pixel is generated and embedded to the LSB of the pixel itself firstly. At the image block level, the image is then partitioned into blocks, and the relation watermark of each block is computed and embedded into the top-left sub-block of its corresponding excursion block in a reversible way. The excursion block mapping sequence can be generated by sorting the keyed chaotic sequence. After all the relation watermarks are embedded, in each block embedded by relation watermark, the detection watermark is computed and embedded into the down-right subblock of the block itself in a reversible way. In the extracting process, the watermarked image is partitioned into blocks, then the embedded detection watermark of each block is extracted and the block itself is partially recovered for the first time. And the embedded relation watermark of each block is extracted and the block is fully recovered for the second time. Then we compute the new relation watermark and detection watermarks of each recovered block and perform comparison with the extracted ones. In the proposed scheme, the tampered watermark can pass the authentication because it does not reduce the value of image to some extent. But if the image content is tampered, the further step is taken at the pixel level to locate tamper to specific pixel by comparing the re-computed location watermark with the extracted location watermark. In the proposed image authentication scheme, the complicated nonlinear property of chaos is utilized to generate the pixel location watermark at the pixel level, construct the excursion block map, and create the relation watermark and de- ection watermark at the image block level. Theoretical analysis and computer simulation have verified the successful achievement of the proposed image authentication scheme.