A novel technique for misalignment parameter estimation in double compressed JPEG images

The Double JPEG problem and its analysis has been attracting research attention since it is a common way of introducing tamper in digital images. Most Double JPEG based forensic methods assume aligned second compression cycle which is referred as the A-DJPEG scenario. However, when copy-move forgery occurs, the second compression cycle is not always aligned w.r.t the first compression cycle. In such cases the misalignment factor in the horizontal and vertical directions need to be estimated which will be very useful for further blocks in the forensic analysis pipeline. This paper presents a novel technique for estimating the degree of misalignment between the first DCT compression grid and the second DCT compression grid with the motivation that such parameters estimation can be utilized for image forensic applications. The proposed technique is compared with an existing state-of-art technique for misalignment estimation utilizing different grid combinations and for several images from the UCID database in order to validate the superiority of the proposed technique.