I'm making a freemium art program for the Mac. One of the pay for features is being allowed to export the file in a non-propietary format. If people were allowed to take screenshots of the canvas in the free version, that'd obviously reduce the number of people willing to pay for the full version. So, does anyone know how I can make a sandboxed app that will distort or block screenshots of its canvas? I'm okay with a non-bulletproof solution, I just want something that reduces the number of people who are content with working around it.