[max99x]

Most pieces are positioned in the middle of a square. A simple way to recognize the color of the piece and its square is to do a flood fill with a bit of tolerance (say 32/256) from the center pixel. The area covered by the flood fill will only contain the pixels making up the piece, while the area outside the flood fill will have pixels the color of the square. Reflections might cause a bit of noise, but a slight gaussian blur should be enough to get over that.