Lifehacker: How to Tell if a Photo Has Been Doctored. “Nearly every photo online has been edited in some way, whether through cropping, filtering, compressing, color-correcting, or other generally innocuous touch-ups. But a lot of people attempt to pass off doctored images as true ones, leading to hoaxes, crackpot theories, and more than one trip to Snopes for some fact-checking. You can do the world a service by helping those around you identify real photos against fake ones. Here’s how…” This is beginner level, but a useful start. Some of the comments are interesting.