[johtso]

Yeah, the transparent board with fiduciary marks and a camera was the road I was going down at one point.

There's also a really neat solution that involves a matrix of wires, one for each row and column, and then running a current through the wires. The pieces then each interact with the current in a unique way producing a signal. You then do some clever stuff to figure out all the pieces that are on a given wire. Cheaper than RFID, and you don't need a sensor for each square and can do some multiplexing. I think it possibly uses magnets in the pieces? You can tell electronics is my strong point!