  Imaging is a sophisticated process combining a plenty of photovoltaic
conversions, which lead to some spectral signatures beyond visual perception in
the final images. Any manipulation against an original image will destroy these
signatures and inevitably leave some traces in the final forgery. Therefore we
present a novel optic-physical method to discriminate splicing edges from
natural edges in a tampered image. First, we transform the forensic image from
RGB into color space of S and o1o2. Then on the assumption of Dichromatic
Reflection Model, edges in the image are discovered by composite gradient and
classified into different types based on their different photometric
properties. Finally, splicing edges are reserved against natural ones by a
simple logical algorithm. Experiment results show the efficacy of the proposed
method.
