Abstract: This paper presents a new block artifact measure of the images local area and a simple method of blind forensic of JPEG forgeries on the basis of analyzing the overall block artifact of the JPEG images. Firstly, we calculate the horizontal and vertical differences maps of the JPEG image, and then divide the two maps into many sub-blocks with a specific size. Secondly, we measure the block artifact of each sub-block on the local area using the new method. Finally, the detection and location of doctored region is realized via checking significant differences of block artifact in different local areas. The experimental results validate the proposed approach in blind detecting the tampered area of the double JPEG compressed images.