Robust and fragile watermarking for medical images using redundant residue number system and chaos

This research discusses a novel watermarking scheme using redundant residue number system and chaos. The salient feature of said research is that image remains fragile while the watermark information is made robust. Image pixels are converted into residues so that the unaided eye could not see the image contents. To make the image invisible to the unaided eye, only the ROI part of image is passed through the Residue Number System thus, to enhance the secrecy of the image. While converting the ROI part of image into residues, there are some residues which exceed eight bits so, these residues are converted to exact eight bits by pertaining some intelligent mechanism. To achieve the robustness of watermark, firstly redundant residues of watermark are made and then the resultant watermark is encoded through error correcting codes. To achieve the fragility of image, hashing technique is utilized. Hash of the entire image but with the residued ROI is combined with the encoded and redundant residued watermark and then resultant watermark is embedded in the Region of non-interest (RONI) zone of native image rooted on the chaotic key in order to enhance the security of the watermark. In case of no tampering, fragile watermark can be successfully recovered as well as exact recovery of the original image but if the image is attacked, the fragile watermark is destroyed while the robust watermark is extracted with better readability.