At present

digital images are suffering a serious credibility crisis. While existing passive forensic techniques are able to successfully detect multiple types of standard image manipulations

many forensic techniques do not account for the possibility that a forger with advanced knowledge of signal processing techniques may attempt to disguise their forgery. As a result

researchers have begun studying anti-forensic operations that are capable of deceiving forensic techniques. This study attempts to review the state-of-the-art image anti-forensic techniques (including rising reasons

implementation principles

technical characteristics

and application prospects) and summarizes the challenges and opportunities associated with anti-forensic techniques. Most studies on passive forensic techniques in image forgeries have focused on identifying different tampered traces and inherent characteristics. The present study examines different characteristics to review and compare previous studies on image anti-forensic techniques. Based on different forensic characteristics

the anti-forensic techniques of digital images are summarized as three research topics:hiding left traces

inherent characteristic forgery

and anti-forensic detection. The related research progress and challenges are surveyed according to different characteristics. Main problems in the current research on image anti-forensic techniques were pointed out

and further research directions are presented.