Microsoft released a new open source SDK today demonstrating how to use a webcam to provide "touchless" multi-touch by tracking the size and position of multiple coloured markers (fingers, toys and pens seem to work just as well!).

The library is what Microsoft describes as a "community" project, written by two Microsoft engineers Ian Sands and Chris Pratley in their spare time - in a similar vein to Google Labs. The source code includes a C++ library for talking to the web cam - but the core of the processing logic is written in C#. Included with the source code is a bunch of sample applications to showcase the technology, including

1. Map - using two markers you can rotate, zoom, and move a map.
2. Defender - a pong-like game
3. Snake - controlling a snake with a marker pen
4. Draw - the marker is used to ... draw!

You can check out more at the Microsoft Office Labs site and download the source code from CodePlex.