Nonorthogonal DCT implementation for JPEG forensics

The detection of JPEG prior compression has become an essential task in the detection of forgery in image forensics. In this paper we propose a novel DCT implementation technique that can be utilized in the detection of any hacking or tampering of JPEG/DCT compressed images. The proposed approach is based upon recent literature ideas of recompressing JPEG image blocks and detecting if this block has been compressed before or not and how many times. In this paper we proposed a DCT implementation that has a onetime signature on processed coefficients or pixels and can be used as a tool to detect if this block has been compressed before using the proposed implementation or not. Any further processing can be easily detected and identified. The proposed DCT transformation is nonorthogonal and results in a minor amount of error due to this nonorthogonality, however it maintains an excellent tradeoff between compression performance, and transform error. Illustrative examples on several processed images are presented with complexity analysis.