关键词: 双量化效应, 盲检测, 直方图, 后验概率, 连通区域

Abstract: The double quantization effect in JPEG images is becoming important clue in detecting image forgeries. As many detection methods are based on the block artifacts of DCT coefficients, a new blind detection scheme which makes use of the double quantization effect is proposed. By comparing two posteriori probabilities of untampered region, which are computed by histogram of DCT coefficients and interval length respectively, a feature that can distinguish the tampered block and untampered block is extracted, and then the feature value of each DCT block is calculated. After setting a threshold, the tampered blocks whose feature values are larger than the threshold are obtained. Finally, the tampered region is located by labeling the connected components. Experimental results demonstrate that the proposed scheme can detect and localize the tampered areas more accurately with respect to previously proposed methods, especially for colorful or rich texture images.

Key words: double quantization effect, blind detection, histogram, posteriori probability, connected region