We describe a photo forensic technique based on detecting inconsistencies in lighting. This technique explicitly measures the 3-D lighting properties for individual people, objects, or surfaces in a single image. We show that with minimal training, an analyst can accurately specify 3-D shape in a single image from which 3-D lighting can be automatically estimated. A perturbation analysis on the estimated lighting is performed to yield a probabilistic measure of the location of the illuminating light. Inconsistencies in lighting within an image evidence photo tampering.