Photo Forensics from Partial Constraints

A variety of forensic methods have been developed to identify falsified photos, each unified by the ability to estimate and detect properties of a photo that are perturbed by forgery. There exist, however, many photos in which the required properties cannot be estimated. We present an approach to detect forgery in these photos. We use this approach to detect physically inconsistent shadows and shading in photos for which it is not possible to estimate the associated lighting properties. Specifically, we develop a method to detect inconsistent shadows cast by point and area light sources when a strict shadow-to-object correspondence cannot be estimated. We further develop a method to detect inconsistencies between shadows and the shading on objects when object geometry is only partially known, and when objects are photographed under unknown perspective. We conclude by describing prior methods that can be generalized to analyze photos in which estimation is not possible.