Anti-forensics of a NAD-JPEG Detection Scheme Using Estimation of DC Coefficients

Bianchi et al. proposed a method to detect the non-aligned double JPEG (NAD-JPEG) compression using the presence of distortions in the Integer Periodicity Map (IPM) of DC coefficients of any JPEG image. However, we found that the IPM can be easily altered without affecting the visual quality of an image. In this paper, we propose a new anti-forensics scheme that alters the IPM to deceive the Bianchi et al. scheme. In our proposed method, a statistical model of the DC coefficients from singly compressed JPEG image is used to generate an estimated image which is free from quantization artifacts that are present in the IPM. The estimated image is subjected to NAD-JPEG compression. It was found that the DC values of NAD-JPEG image are no longer be the multiples of the corresponding primary quantization step size \(q_1\). As a result, the DCT coefficients do not cluster around the lattice related to the \(q_1\) and the IPM of the double JPEG compressed image seems to be the IPM of a singly compressed JPEG image. Experimental results show the effectiveness of the proposed anti-forensics scheme as the accuracy of the said forensics method get reduced to less than \(50\%\) in case of anti-forensically modified images.