Content-based Multi-zone Tamper With The Image Authentication

Accompanying the rapid development of multimedia technology, a lot of image processing devises and software are being used widely, it is easy to process digital images, hostile tamper and transmitting will cause critical harm to society and people. So image authentication becomes a very hot study topic in the world. It aims at distinguishing normal operations and malicious tampers, detects and locates the tampered areas effectively.The paper mainly researched image authentication which based on digital signature, focused on analyzing approaches of measuring tampers that happened more than one region and how to enhance the probability of tamper detecting, the main content and contributions of this paper are:1. A new method of distilling m bits abstract from the binary information sequence with the length of n=2m-1 is proposed based on the coset decomposing theory of error correcting code. The authentication abstract obtained by this method is highly sensitive to the changes of the feature data, compare with the method of using hash function, this method is simple and flexible, and can obtain shorter abstract.2. An important conclusion is proved, distortion of image blocks' mean value caused by JPEG lossy compression has a superior bound, and then a new image pre-processing method based on this conclusion is introduced and analyzed; After analyzing the influence of JPEG compression to the DCT coefficients, a new method of pre-processing the image is proposed based on pre-quantification.3. Two new image authentication schemes based on digital signature are proposed in this paper, they can distinguish JPEG loss compression and malicious tampering under the condition of QF≥25 and QF≥40 respectively. When more than one region are tampered, these two schemes not only detect and localize the tampered area effectively, but also have higher probability of tamper detection and lower false alarm probability. The result of theory analysis and simulation show that these two schemes are correct and effective.