I came across a good site yesterday called Photoshop Disasters. The blog shows all the mistakes that leading magazines, newspapers and ad companies make when promoting a product.
50 years ago I imagine that it was only goverment agencies like the CIA who did photo editing but if you pick up any magazine nowadays it's difficult to find a picture which hasn't been cropped, changed or manipulated in some way. Which is why I enjoy this blog so much. It's suprising some of the pictures which have slipped through the net and made it onto the front page.
Link : Photoshop Disasters