1. A method for detecting local motion in a series of image frames, wherein each image frame comprises a plurality of pixels, the method comprising: receiving a first image frame and a second image frame in the series of image frames, wherein the second image frame is later in time relative to the first image frame; reading values of a first plurality of pixels at first pixel locations of the first image frame, wherein the first plurality of pixels is a subset of the plurality of pixels in the first image frame; reading values of a second plurality of pixels at second pixel locations of the second image frame, wherein the second plurality of pixels is a subset of the plurality of pixels in the second image frame, wherein the first pixel locations of the first image frame correspond to the second pixel locations of the second image frame; calculating a first delta function to produce a first output, the first delta function comprising a sum of differences between pixel values of corresponding pixel locations of the first plurality of pixels in the first image frame and the second plurality of pixels in the second image frame; comparing the first output to a first one or more thresholds, determining if local motion has occurred in the second image frame based on said comparing.