Abstract: A system detects motion in a video signal by identifying differences between a current image frame and a reference image frame. A difference profile is calculated that represents the differences between the current image frame and the reference image frame. A motion detection signal is generated by the system if the difference profile exceeds a threshold. In one configuration, the system replaces the reference image frame with each successive current image frame. In other configurations, the system replaces the reference image frame with the current image frame if the difference profile exceeds the threshold. The system generates difference data associated with the differences between the current image frame and the reference image frame. This difference data can be partitioned into multiple blocks. An average value is calculated for each block of difference data.