“ A more advanced form of analysis might focus on the lighting in the photos to see if there were inconsistencies in the images’ shadows or lighting gradients. (See, for example, this forged photo of John Kerry and Jane Fonda, where one calculation (PDF) pegged the light coming from 123 degrees onto Kerry and 86 degrees onto Fonda.) Another technique used to spot composite photographs looks at the way light reflects off a subject’s eye to determine exactly where the light was coming from. Professional retouchers say they can also recognize where a photo has been altered if the skin texture is too smooth or the model’s symmetry too perfect, or if the perspective appears distorted."