There's a great article by Errol Morris in the New York Times about the power of photography to deceive even the mainstream media. It includes lots of examples from recent times, and interviews with a couple experts in visual propaganda.

One quote that I like a lot is this, by the author:

"If you want to trick someone with a photograph, there are lots of easy ways to do it. You don’t need Photoshop. You don’t need sophisticated digital photo-manipulation. You don’t need a computer. All you need to do is change the caption."

Good reading.