Phase based detection of JPEG counter forensics

Many recent techniques for forgery detection tried to counter noise dithering, which is considered to be the most successful technique for removing footprints of JPEG editing in countering forensics. In this paper we propose a novel idea of detecting any noise dithering that is typically adopted in removing footprints in counter anti forensics of images. This technique is based on detecting phase variations for DCT coefficients, for decoded JPEG images. We try to measure the level of coherence of phase values for coefficients and detect thresholded variations that would indicate some editing or tampering of images. The proposed technique is robust against noise dithering due to the fact that local homogeneous regions inherit distinctive phase values. These phase values are inconsistent with embedded or dithered noise signals that are considered to be out of phase and can be easily detected in noisy environments. Our proposed technique is compared with literature techniques for performance in noisy applications.