As one of the most important topics in image forensics, resampling detection has developed rapidly in recent years. However, the robustness to JPEG compression is still challenging for most classical spectrum-based methods, since JPEG compression severely degrades the image contents and introduces block artifacts in the boundary of the compression grid. In this article, we propose a method to estimate the upscaling factors on double JPEG compressed images in the presence of image upscaling between the two compressions. We first analyze the spectrum of scaled images and give an overall formulation of how the scaling factors along with the parameters of JPEG compression and image contents influence the appearance of tampering artifacts. The expected positions of five kinds of characteristic peaks are analytically derived. Then, we analyze the features of double JPEG compressed images in the block discrete cosine transform (BDCT) domain and present an inverse scaling strategy for the upscaling factor estimation with a detailed proof. Finally, a fusion method is proposed that through frequency-domain analysis, a candidate set of upscaling factors is given, and through analysis in the BDCT domain, the optimal estimation from all candidates is determined. The experimental results demonstrate that the proposed method outperforms other state-of-the-art methods.

中文翻译：

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双 JPEG 压缩图像放大因子的鲁棒估计


作为图像取证中最重要的课题之一，重采样检测近年来发展迅速。然而，对于大多数经典的基于频谱的方法来说，JPEG 压缩的鲁棒性仍然具有挑战性，因为 JPEG 压缩严重降低了图像内容，并在压缩网格的边界引入了块伪影。在本文中，我们提出了一种在两次压缩之间存在图像放大的情况下估计双 JPEG 压缩图像的放大因子的方法。我们首先分析缩放图像的频谱，并给出缩放因子以及 JPEG 压缩参数和图像内容如何影响篡改伪影外观的总体公式。分析得出五种特征峰的预期位置。然后，我们分析了双JPEG压缩图像在块离散余弦变换（BDCT）域中的特征，并提出了一种用于放大因子估计的逆缩放策略并给出了详细的证明。最后，提出了一种融合方法，通过频域分析，给出候选的放大因子集，并通过BDCT域的分析，确定所有候选的最佳估计。实验结果表明，所提出的方法优于其他最先进的方法。