Images may be acquired by cameras and processed to detect the presence of objects. Described are techniques to use rectified images for further processing such as object detection, object identification, and so forth. In one implementation, an image from a camera is processed to produce a rectified image having an apparent perspective from overhead. For example, the rectified image may be an image that appears to have been obtained from a virtual camera that is above the shelf and having a field-of-view that looks downward. The rectified image may be an orthonormal projection of pixels in the acquired image, relative to a plane of the surface upon which the objects are resting.