Hammer nail through a wooden ruler. Hang picture on that nail. Line it on the wall where you want it. Remove picture, push in nail to make an indent. Remove ruler, hammer another nail into the wall Hang your perfect picture up.
Where have you been all my life? Pop top as picture hanger. Ive done this for years, started it in college when I didnt have hangers too lazy to get some. Why do that when you have all those leftover beer cans.and an idea.