I have a scanned image of a book page and i need to crop this scan for leaving only page area. I tried to use AForge to detect page borders, but it doesn't work because the space which i need to crop may consist of little "light" areas (due to scanner quality) and edge detector detects borders there. That's why this is bad idea as for me. Could you recommend something? P.S. Please don't tell me to use non-free libraries.