How to Tell if a Digitial Image Has Been Altered

An article at Photoshop News asks the question: How do you tell if a digital image has been altered? With a trained eye, I answer. Physically impossibilities are a clear giveaway. A penguin and a camel in the same ad, for example, on a frozen tundra isn't 'normal' and therefore is a clear giveaway. I always look at the shadows and edges to see how well the author made selections and added shadows that weren't there before. Highlights will also be a clear indication of an original as well as film grain. It's difficult to completely match the texture, colors, and lighting of one photo to the next, although it's easier to fake it within the same source image. The more subtle the changes the better.

It's a lot like spotting digital effects as opposed to live action shots. Throughout the Star Wars trilogy, you can see mattes behind TIE fighters as they fly through space and you can tell when an actor was shot against a blue screen. Lucas used a bunch of rudimentary techniques to get the job done, including rubbing vasoline on the film to make Luke's landspeeder look like it was floating. The Lord of the Rings movies were much better, but you can still spot what's live and what's fake, even without watching the special features on the DVD. In Two Towers, when Treebeard picks up Merry and Pippin, you can see the oddity in the colors of the CG character juxtaposed with the studio lighting on the live characters. Still, there are some sequences that are completely CG and you just can't tell what's what, as when Legolas climbs up the Oliphant on arrows and takes the whole thing down.

What's been amazing in terms of the blending of CG with live action is the really sublime shots inMinority Report and more recently in The War of the Worlds. Spielberg makes every attempt to blur the line between live action and CG by using the simplest things: light, shading, and environmental effects.

Bending reality with Photoshop can be easy, but make it look real is a whole other story.