I think finger position sensors would be more ideal than camera recognition, since there are many times your fingers could become obfuscated behind other finger

I think finger position sensors would be more ideal than camera recognition, since there are many times your fingers could become obfuscated behind other fingers or if you rotate your hand. RFID tags are cheap and can use passive power. I imagine with a bracelet transmitter and positioning device they could be tracked in real time and attached to the finger tips using a reusable adhesive. Should require minimal calibration and then would allow for new touch inputs for almost any device that is calibrated along with it. Could even make regular monitors touch screen.