I just finished replacing backgrounds on 101 portraits for many Nestle Power Point presentations. I recognized many as those I have shot but some had trees and buildings behind so I assume they were scanned from prints. The one trouble I had was that they were all tiny 72dpi jpgs. I used Photoshop CS5's quick select tool and refine selection brush. That and an identical gradient made all of the power point images look the same.
I tell my studio lighting students that in 2011 each and every photographer has to know Photoshop so that they can pre-vision a shot and know how Photoshop can help them. I used to shoot Oreo's in ice cream. Oreos demand a certain light and ice cream needs something different, By knowing that one can light the ice cream beautifully and shoot first, then replace the lights for the Oreo and shoot secondly you can have both lit perfectly and put together in one final shot. Remember; you get paid if you light and shoot or retouch. Most of my earning this February has been from retouching. Thank God. Thank Adobe.