A passive forensics method to detect tampering for double JPEG compression image is proposed. In the proposed method, inconsistency of quality factors is used to detect double JPEG compression, and then a passive forensics approach to detect tampering and locate tampered area for tampered JPEG images is proposed. Comparing with existing methods, the main advantages of the proposed method are as follows: (1) It can detect rotation, scaling and tampering in small area. (2) It has a high computing efficiency.