I am working on a project in which I am attempting to analyze a fish within a petri dish using ImageJ and an AVI clip of the fish under a microscope. My first hurdle is to locate the fish within the dish, which I assume I could do without even needing the entire stack (maybe even just a single frame). I am new to image processing, but with the libraries available in ImageJ, I am hoping to be able to locate the edge of the fish and either cut out that edge or cut out a smaller box containing just the fish. Any help would be greatly appreciated from those of you with experience in either ImageJ or image processing in general. Thanks!