| With the widely use of digital cameras, digital images have already become a part of our daily life. However, the credibility of digital images has faced severe challenges in the digital era caused by the intrinsic nature of easy modification of digital data as well as the powerful function of modern image process software. Due to the requirements of application and technology mentioned above, this thesis mainly studies the detection methods for testing the regional duplication and forgery that is part of passive digital image authentication.Passive digital image authentication is a technology of detecting image authenticity and source without relying on any pre-extracted or pre-embedded information. And Regional duplication forgery is an important branch of passive digital image authentication. In this thesis, apart from study the passive authentication theory which has been proposed currently, we also study Tchebichef moments invariants as well as characteristics of the SIFT feature point starting with left traces of the process of digital image forgery. We designed a corresponding passive authentication algorithm. It can detect the duplication region in the forgery image. In this paper, research work is conducted as follows:Firstly, combine with domestic and foreign passive digital image authentication methods; we make an in-depth study of the relevant technology, and do some research on theoretical models and systems framework about digital image forensics. In summary on the basis of previous work, passive authentication framework tampering regional replication and geometric model of the deformation zone transfer tampering are designed according to existing theories.Secondly, this paper designs a new passive digital image authentication algorithm in the basis of Tchebichef Moments Invariants algorithm to detect and identify the location of image copy-move tamper, in which an object region in the image is copied and pasted somewhere else in the original image to confound right and wrong. After reducing the image dimension by Discrete Wavelet Transform (DWT), the Tchebichef moments invariants is applied to the fixed sized overlapping blocks of a low-frequency image in the wavelet sub-band, and the eigenvectors are lexicographically sorted. Then, similar eigenvectors are matched by a certain threshold. Finally, the forgery part is identified by the threshold. The experimental results show that proposed method can not only localize the copy forgery regions accurately, but also undergo some attacks like random noise contamination, lossy JPEG compression, rotation transformation etc., and reduce the amount of computation, which improves the detection effectively.Thirdly, according to the feature that feature points does not match one another in the same natural image, a passive algorithm of digital image, based on its own feature point, has been designed, which can resist geometric transformation and be used in testing the type of region duplication forgery in the digital image. The algorithm firstly extracts the image feature points, calculates the corresponding eigenvectors, and then divides the feature vector sets and matches them, the image matching point's pairs marked with the connections. If the image is copied tampered with, the tag will clearly focus on certain edges between the two regions. If the image has been duplicated, the lines of marks will be clearly focused on certain edges between the two regions. Finally, the simulation experiment verifies the effectiveness of the algorithm of digital image region duplication forgery, which can resist geometric transformation.Finally, summarizes the work done for the problems of work and areas for improvement, as well as the direction of future work. |
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