Patent ID: 8295541

Claim:
A method of detecting change of state of an object scene containing an object of interest, the method comprising: a) obtaining a reference image of the object scene containing the object; b) analyzing the reference image to detect edges corresponding to at least the object; c) determining a reference set of points corresponding to a plurality of edges detected in the reference image; d) obtaining a subsequent image of the object scene; e) analyzing the subsequent image to detect edges; f) determining a subsequent set of points corresponding to a plurality of edges detected in the subsequent image; g) comparing a position of points in the reference set of points relative to a position of points in the subsequent set of points; and h) in the event that a result of step (g) meets at least one predefined criterion: determining that there is a change in position of at least one point within the subsequent set of points relative to the reference set of points; and commencing an alarm counter for triggering an alarm.