Median filtering detection using variation of neighboring line pairs for image forensics
Abstract. Attention to tampering by median filtering (MF) has recently increased in digital image forensics. For the MF detection (MFD) this paper presents a feature vector that is extracted from two kinds of variations between the neighboring line pairs: the row and column directions. Of these variations in the proposed method, one is defined by a gradient difference of the intensity values between the neighboring line pairs, and the other is defined by a coefficient difference of the Fourier transform (FT) between the neighboring line pairs. Subsequently, the constructed 19 dimensional feature vector is composed of these two parts. One is the extracted 9 dimensional from the space domain of an image and the other is the 10 dimensional from the frequency domain of an image. The feature vector is trained in a support vector machine classifier for MFD in the altered images. As a result, in the measured performances of the experimental items, the area under the receiver operating characteristic curve (AUC, ROC) by the sensitivity (PTP: the true positive rate) and 1 specificity (PFP: the false positive rate) are above 0.985 and the classification ratios are also above 0.979. Pe (a minimal average decision error) ranges from 0 to 0.024, and PTP at PFP=0.01 ranges from 0.965 to 0.996. It is confirmed that the grade evaluation of the proposed variation based MF detection method is rated as "Excellent (A)" by AUC is above 0.9.
J. Electronic Imaging