Nowadays images have become an important form of expression for data communication. However, if the images get tampered during the communication, their usefulness is undermined and the resending of images can bring unnecessary workload to network. Therefore,it is quite an important issue to maximize the usefulness of images even if the images have been tampered. To assure the authenticity and usefulness of images that have been tampered, this paper used modified Du et al.'s first level rehash to propose an image self-verification scheme. To increase the usefulness of tampered images, we manage to precisely identify which 'pixels' of the tampered images have been tampered. The rightmost two bits of every pixel are used to store the authentication information, which was derived by means of the modified HIT construct procedure proposed in modified Du at al.'s first level rehash. Before sending images, both of receiver and sender have to determine a secure key SK and several hash functions, and then the senders can calculate the HIT value first and embed the value to the rightmost two bits of every pixel to generate an image containing self-verification information. Upon receiving such images, the receivers can conduct the same procedure to calculate the HIT values for the authentication. As the authentication information is directly embedded in the images, no extra transmission cost will occur. Thus, our scheme will hot increase transmission cost and is considerably convenient in real practice as there is no special limitation on the hash function used in our scheme.
