Median filtering detection based on variations and residuals in image forensics

Abstract

To attain a robust feature vector for median filtering detection (MFD) in digital forgery images, this paper presents a short feature vector that is made up of three types of feature sets. The first set is defined by the variation to be the 3-D length in the gradient difference of the intensity values of the adjacent row and column line pairs in the image, respectively. The second set is defined by the variation in the coefficient difference of the Fourier transform to be the 3-D length in the adjacent line pairs. The last set is defined by the residual image between an image and its reconstructed image by the gradient based on solving Poisson's equation, which is also the 3-D length. Two of the sets are extracted in the spatial and spectral domains of an image, respectively, and the last set is extracted from the residual image. The totally formed 9-D feature vector is subsequently trained in the support vector machine classifier for MFD. In the experimental results of the proposed variation- and residual-based MFD scheme, the area under the curve is achieved closer to 1. Despite a short feature vector, the evaluation of the proposed MFD scheme is graded as "Excellent (A)". In particular, the scheme detected good median filtering from the JPEG post-compression image for the cut-and-paste forgery image.