Digital Forensics: 5 Ways to Spot a Fake Photo

This image has been modified in several places. The digital forensic techniques described on the following pages could be used to detect where changes were made. Image: SciAm Staff

Supplemental Material

• Overview Digital Forensics: How Experts Uncover Doctored Images
• Infographic Altered Lance Armstrong Photo Explained
• Photo Album Photo Tampering Throughout History [Slide Show]

This story is a supplement to the feature "Digital Forensics: How Experts Uncover Doctored Images" which was printed in the June 2008 issue of Scientific American.
Lighting
Composite images made of pieces from different photographs can display subtle differences in the lighting conditions under which each person or object was originally photographed. Such discrepancies will often go unnoticed by the naked eye.
For an image such as the one at the right, my group can estimate the direction of the light source for each person or object (arrows). Our method relies on the simple fact that the amount of light striking a surface depends on the relative orientation of the surface to the light source. A sphere, for example, is lit the most on the side facing the light and the least on the opposite side, with gradations of shading across its surface according to the angle between the surface and the direction to the light at each point.