A second look at first significant digit histogram restoration

We analyze a class of first significant digit (FSD) histogram restoration techniques designed to cover up traces of previous JPEG compressions under a minimum cost constraint. We argue that such minimal distortion mappings introduce strong artifacts to the distribution of DCT coefficients, which become particularly prevalent in the domain of second significant digits (SSDs). Empirical findings from large image databases give insight into SSD distributions of DCT coefficients of natural images and demonstrate how images that underwent FSD histogram restoration deviate from natural images.