Passive detection of doctored JPEG image via block artifact grid extraction

It has been noticed that the block artifact grids (BAG), caused by the blocking processing during JPEG compression, are usually mismatched when interpolating or concealing objects by copy–paste operations. In this paper, the BAGs are extracted blindly with a new extraction algorithm, and then abnormal BAGs can be detected with a marking procedure. Then the phenomenon of grid mismatch or grid blank can be taken as a trail of such forensics. Experimental results show that our method can mark these trails efficiently.