1. A detector comprising: a sensor for collecting electromagnetic energy from a field of view for the sensor, the sensor generating a signal indicative of objects in the field of view; an image analyzer electronically coupled to the sensor for receiving the sensor signal and forming an image of pixels therefrom; an edge detector adapted to detect an edge of an object depicted within the pixel image, and determining the position of the edge within the pixel image; a data storage device for storing edge location data of a first image; and a comparator for comparing edge detection data from a second image to edge detection data from the first image in order to determine if the object associated with the edge has moved since the acquisition of the first image.