1. Introduction
Nowadays, the authenticity and integrity of a digital image can hardly be determined visually due to the powerful and sophisticated image edition tools, which makes digital image forensics more important. Since JPEG is the most widely used format in image communication and storage, double JPEG compression (DJPEG in short) detection has become an important branch in image forensics. Such kind of approaches assume that the original image is usually JPEG compressed once in the imaging stage and the modified image usually undergoes at least two JPEG compressions.