Abstract: Methods and devices for processing captured video frames to detect specific changes observable in video using three consecutive video frames. The images in the first video frame are compared with the second frame and the images of the second frame are compared with the third frame to produce two intermediate images which show the first order change observable in video. These interim images are then analyzed. A geometric transformation is found such that when the transformation is applied to one of these intermediate images, the number of pixels which match between the interim is maximized. This geometric transformation, which may include a linear as well as a rotational component, is then applied to one of the intermediate images to result in a transformed image. The transformed image is then subtracted from the other intermediate image to arrive at an end image which shows the second order change or the change in a change observable in video.