This will sound wacky, but I have a movie of maggots moving (honest!) and need to highlight a couple of the little devils as they move around on an agar plate, for example by superimposing a ring around them, or graying out the rest of the image except for a circle around them (the kind of thing they do on the football on TV). Is there any way of doing this with standard or free/cheap software? EDIT: NB I mean on the video, not on the presentation - someone has introduced me to Mouseposé, which does exactly that during a presentation. I want to do that effect on the movie.