Inter-channel demosaicking traces for digital image forensics

Digital image forensics seeks to detect statistical traces left by image acquisition or post-processing in order to establish an images source and authenticity. Digital cameras acquire an image with one sensor overlayed with a color filter array (CFA), capturing at each spatial location one sample from the three necessary color channels. The missing pixels must be interpolated in a process known as demosaicking. This process is highly nonlinear and can vary greatly between different camera brands and models. Most practical algorithms, however, introduce correlations between the color channels, which are often different between algorithms. In this paper, we show how these correlations can be used to construct a characteristic map that is useful in matching an image to its source. Results show that our method employing inter-channel traces can distinguish between sophisticated demosaicking algorithms. It can complement existing classifiers based on inter-pixel correlations by providing a new feature dimension.