A new semi-fragile watermarking algorithm for image content authentication based on chaotic mapping is presented.Chaotic sequence generated from the block itself by means of Logistic mapping is used to generate watermarking embedding;then the generated watermarking information is embedded into LSB plane of another image block with Torus Automorphism mapping,which the corresponding relation is determined by the secret key to establish the correlation among the image blocks.The results show that the method could localize the tampered watermarked image by using the high sensitivity on initial value of the chaotic mapping without host image in watermark extraction.Moreover,watermarked images obtained have good subjective quality,precise localization of tampered areas,and the algorithm is simple and safe.