A method of detecting whether a user is in close proximity to an end point. A base video frame of the end point is captured when the user is not in close proximity to the end point. A current video frame of the end point is captured and compared to the base video frame of the end point to determine whether...http://www.google.es/patents/US5892856?utm_source=gb-gplus-sharePatente US5892856 - Method of presence detection using video input
