Given a JPEG pipeline (compression or decompression), this paper shows how to find the antecedent of a 8 x 8 block. If it exists, the block is compatible with the pipeline. For unaltered images, all blocks are always compatible with the original pipeline; however, for manipulated images, this is not always the case. This article demonstrates the potential of compatibility concepts for JPEG image forensics. It presents a solution to the main challenge of finding a block antecedent in a high-dimensional space. This solution relies on a local search algorithm with restrictions on the search space. We show that inpainting, copy-move, or splicing applied after a JPEG compression can be turned into three different mismatch problems and be detected. In particular, when the image is re-compressed after the modification, we can detect the manipulation if the quality factor of the second compression is higher than the first one. Our method can pinpoint forgeries down to the JPEG block with great detection power and without False Positive. We compare our method with two state-of-the-art models on localizing inpainted forgeries after a simple or a double compression. We show that under our working assumptions, it outperforms those models for most experiments.

翻译：给定一个JPEG处理流程（压缩或解压缩），本文展示了如何寻找一个8×8图像块的前驱块。若该前驱块存在，则此图像块与该处理流程兼容。对于未经篡改的图像，所有图像块始终与原处理流程兼容；然而对于经过篡改的图像，情况并非总是如此。本文论证了兼容性概念在JPEG图像取证中的潜力。针对在高维空间中寻找图像块前驱这一核心挑战，本文提出了一种解决方案。该方案采用局部搜索算法，并对搜索空间施加约束。我们证明，在JPEG压缩后进行的修复、复制-移动或拼接操作可转化为三种不同的失配问题并被检测。特别地，当图像在篡改后经过重新压缩时，若第二次压缩的质量因子高于第一次，我们即可检测到篡改操作。本方法能以极高检测能力精确定位至JPEG图像块级别的伪造痕迹，且不产生误报。我们将本方法与两种先进模型在单次或双重压缩后定位修复伪造的能力进行比较。结果表明，在我们的工作假设下，本方法在多数实验中性能优于对比模型。