Where should you sit to watch a movie?

A picture viewed from its center of projection (CoP) generates the same retinal image as the original scene. When a picture is viewed from other locations, the retinal image specifies a different layout and shapes, but we normally do not notice the changes. The mechanism underlying this is unknown. We studied the perceived shapes of pictured ovoids and planes while varying viewing angle and the angle by which the pictures were projected. We also varied the viewer's information about the orientation of the picture surface. Viewers compensated nearly veridically for oblique viewing when binocular information for surface orientation was available. In so doing, they used an estimate of local surface orientation and not prior information for object shape nor geometric information in the picture. We present a model that explains invariance for incorrect viewing positions, and other phenomena like perceived distortions with wide fields of view.