Exposing Photographic Splicing by Detecting the Inconsistencies in Shadows

As sophisticated photo editing software is increasingly available and the widespread use of multimedia social network, the reliability of digital images becomes more and more important. Photographic splicing, herein defined as a cut-and-paste of image regions from one image onto another image, is difficult to be detected due to the absence of a reference object. To carry out such forensic analysis, we present a novel shadow-based method, with which the fake shadow of the composites can be detected. We show how to estimate the shadow scale factors with a shadow removal technique and, further, how to estimate the growth rate of the penumbra width (GRPW). Inconsistencies in the shadows are then used as evidence of tampering. Compared with other shadow-based forensic methods, the proposed method can not only deal with the problem of shadow cloning in the same image, but also expose the fakery containing the real shadow, which benefit from the estimation of shadow scale factors and GRPW. Comparison results obtained from the splicing forgery detection database verify the ability of our approach.