1. A computer-implemented process for locating an object to which a device is rigidly attached, comprising: capturing images of the device and the object to which it is rigidly attached; finding image motion features in the captured images; in a common coordinate system, matching device motion features measured by at least one sensor on the device with the image motion features in the captured images of the device; computing on a per pixel basis the difference between the image motion features and the device motion features at a number of pixel locations in one or more of the captured images; and determining the presence of the device and any rigidly attached object in an image as the location of the smallest difference in the coordinates of the common coordinate system.