The cost of jpeg compression anti-forensics

The statistical footprint left by JPEG compression can be a valuable source of information for the forensic analyst. Recently, it has been shown that a suitable anti-forensic method can be used to destroy these traces, by properly adding a noise-like signal to the quantized DCT coefficients. In this paper we analyze the cost of this technique in terms of introduced distortion and loss of image quality. We char-acterize the dependency of the distortion on the image statistics in the DCT domain and on the quantization step used in JPEG compres-sion. We also evaluate the loss of quality as measured by means of a perceptual metric, showing that a perceptually-optimized version of the anti-forensic method fails to completely conceal the forgery. Our conclusion is that removing the traces of the JPEG compres-sion history could be much more challenging than it might appear, as anti-forensic methods are bound to leave characteristic traces. Index Terms — digital image forensics; anti-forensics; JPEG compression 1