Near optimal detection of quantized signals and application to JPEG forensics

In this paper, we investigate the problem of deciding whether a multidimensional signal has been quantized according to a given lattice or not. Under an infinite variance assumption, we derive the expression of the optimal detector, together with a practical approximation formula based on multidimensional Fourier series. As a forensic case study, the proposed detector is applied to the detection of nonaligned double JPEG compression. Results on both synthetic signals and real JPEG images show interesting properties of the proposed detector. Namely, the detector outperforms existing state-of-art detectors for nonaligned double JPEG compression. The application of the proposed scheme to other forensic problems seems a natural extension of this work.