Light and Shadows

If the shadows or light don’t seem to be falling correctly on the subject or in the background, there’s a good chance editing has taken place. Sometimes, there won’t be any shadow visible at all when there should be, which is an easy way to tell if a photo’s been doctored.

Distortions

Zooming in on the pixels can reveal distortions when images are altered — for instance, the edges of a subject may be too stark against the background. Also, unnatural smoothness in a photo with a single color could mean something was painted or blended over.

EXIF Data

EXIF data is information about the image that is saved when a photo is taken, such as the aperture, shutter speed, and ISO, and can indicate how the photo should look. It will also list if a program was used with the image, including photo-editing software like Photoshop.