In 1964, the Warren commission concluded that John F. Kennedy had been assassinated by Lee Harvey Oswald. This conclusion was based in part on the famous “backyard photograph” of Oswald holding a rifle and Marxist newspapers. A number of people, including Oswald himself, have claimed that the photograph was forged. These claims of forgery have been bolstered by what appear to inconsistencies in the lighting and shadows in the photo.
This is but one of several cases in which accusations of photographic inauthenticity have spawned national or international controversies and conflicts. Because these claims are often based on perceptual judgments of scene geometry, we have examined the ability of observers to make such judgments. To do this, we rendered scenes that were either internally consistent or internally inconsistent with respect to their shadows, reflections, or planar perspective distortions. We then asked 20 observers to judge the veridicality of the scenes. The observers were given unlimited viewing time and no feedback. Except for the most degenerate cases, performance was near chance, even though the information required to make these judgments was readily available in the scenes. We demonstrate the availability of this information by showing that straightforward computational methods can reliably discriminate between possible and impossible scenes.
We have used computational methods to also test the claims of inauthenticity made about the Oswald backyard photo. By constructing a 3D model of the scene, we show that the shadows in the photo are consistent with a single light source. Our psychophysical results suggest that the claims to the contrary arose because human observers are unable to reliably judge certain aspects of scene geometry. Accusations of photo inauthenticity based solely on a visual inspection should be treated with skepticism.