From: http://codeninja.de/laserpointergestures/

Just watch the video there. May uses for this simple technique. comeback read below to see how it is done.

By Martin (19.12.06 09:23)
I started looking at this as I would love to have this stuff running on my computer.
DirectShow.net gives you access to the images coming in from your webcam. You need to process each frame and look for the brightest point in each image.
http://directshownet.sourceforge.net/

Once you have those points you can feed them into some gesture recognition code. Here are somelinks to source code that deals with mice gestures.
http://www.smardec.com/products/mouse-gestures.html
http://www.codeproject.com/cpp/gestureapp.asp