http://sourceforge.net/projects/avicaptcl
Video for Windows extension. Capture video from your webcam and interface it to anything using Tcl.
Unfortunately the main page at http://avicaptcl.sourceforge.net/ has been defaced, but the files can still be downloaded from the first link.
Haven't seen this extension used much on the wiki, but I think it's going to be a real hoot to play with it ;)
--Ro 2005-11-26
PT 2005-Nov-27: It might be worth noting that Video for Windows is the old set of APIs and has been replaced by DirectShow which is part of the DirectX stuff.
See also: Webcams / Digital Cameras