Abstract: Passive image forensics，a technology of detecting image authenticity and source without relying on any pre-extraction or pre-embedded information，has become a hot topic with broad prospect in multimedia security.Blind detection of doctored JPEG images is one of the most important issues in digital forensics and has become a hotspot in recent years.It can be classified into three kinds.One is the identification of bitmap compression history and estimation of primary quantization matrix.The others are detecting forgeries by measuring inconsistencies of blocking artifact and detection of composite images based on double compressed JPEG images.In this paper，a full discussion of three kinds are devoted，and has a prospect of future research directions.