Two image tools I recommend to all fellow art lovers: "crop" and "lighten." The former allows you to focus on the most lively parts of your image, and cut out expanses of boring (and difficult) sky, wall, trees, etc. The latter lets you shine a light on your picture, making details easier to see. As an incipiently elderly Englishwoman, my favourite pictures for puzzles are classical works of art – with enough going on that every piece is recognizable to a keen eye.