Abstract: Based on the theory of compressed sensing, a new algorithm is proposed. The tampering can be positioned to block-level based on block certification, and with high positioning accuracy. Algorithm firstly divides the image into several blocks, and block size can be changed from tampering with positioning, then observed value of each block to obtain the observations compression. In the observational domain, we will get the observed value of LDPC code to generation watermark, and the watermark is embedded into the block in the image. Watermark extraction, compressed sensing theory will be used random projection image, and decoding the extracted watermark. Compared with before, it has realized the image tampering detection and image authentication. According to the experimental result, the algorithm has the local tamper detection function, good concealment algorithm. This algorithm is simple and more secure.