Blind Authentication of Resampled Images and Rescaling Factor Estimation

The rapid growth of image processing softwares and advancement in digital cameras has given rise to large amount of doctored images with no obvious traces. When altering an image like copy - paste or splicing to conceal traces of tampering, it is often necessary to resize the pasted portion of the image. The resampling operation may highly likely disturb the underlying inconsistency of the pasted portion, that can be used to detect the forgery. In this paper, an algorithm is presented that can blindly detect rescale operation and estimate the rescaling factor in zoom-in or zoom-out using properties of the zero-crossings of the second difference of the tampered image. Experimental results have proved the validity of the algorithm under different interpolation schemes.