Now that everyone is on the multi-touch bandwagon new systems are popping up all over. Seth Sandler’s solution is fairly ingenious. It uses a piece of paper and a camera to create a camera-based multi-touch interface. All you need is a box, a webcam, and some graph paper and he even includes the demo and application source code.
The system can be used to demo multi-touch functionality or to actually drive a Windows cursor around the screen. He estimates it costs about $5 to $50, depending on the quality of box and camera you use. FinestFones has also discussed using a Bluetooth connected Nokia N95 phone to do this as well.