1. A method practiced using a user's camera-equipped portable computer system, including the acts: processing imagery of a subject captured by the user's camera-equipped portable computer system, to produce processed image data corresponding to a spatial excerpt of the captured imagery, the spatial excerpt comprising less than all of a captured image frame; sending the processed image data corresponding to the spatial excerpt to a remote processor; receiving from the remote processor an estimate of a viewing angle of the camera relative to the subject; and further processing image data corresponding to the captured image frame, in accordance with said estimate of the viewing angle received from the remote processor.