Video processing comprises storing data relating to images of a video signal captured over at least a reference period relative to a current image of the video signal; comparing the current image with a reference image of the video signal captured within the reference period, so as to detect image features in the current image representing changes with respect to a corresponding position in the reference image; detecting whether a detected image feature in the current image has remained at substantially the same image position over a group of images preceding the current image; and displaying the current image with an indication of any such image features and an indication of the duration of the presence of the image feature at that image position.