I have worked in machine vision projects in past. It's not going to be easy to recognize the pieces as is; I suggest that you use 2D pieces for chess. Even better, use some unique design like this one: http://www.chess.com/forum/view/general/experimental-chess-s...
Agree that it will be tricky to recognize the pieces, but what's the point in doing it with 2D pieces? The app would be (slightly) more exciting if it could help you record the state of any game anywhere in less than 5 seconds -- and allow you to continue playing online.
I suggested 2D if he wanted to build a system for himself. May be multi-angle snap-shots or a video capture could be processed for capturing conventional chess boards. But even that would not work for all chess-boards. I have come across some pieces that are different to distinguish.