Puzzles with the same exact visuals should be interchanged

[Stephcraft]

In most cases this applies to solid color pieces but also to matching pieces. Take this puzzle for instance:

An all black image with many matching puzzle pieces. Currently only the puzzle with the assigned position on board [x, y] will be valid. But an additional check should be made to see if the puzzle's texture is matching. This check should be optimized, as image manipulation is usually quite slow.