This demonstrates augmentation of a generic picture postcard with video in realtime. As opposed to using special image markers for tracking (as with ARToolKit) this form of augmentation can be applied to any complex image. The postcard is tracked using a standard webcam and The Artvertiser software.
Here's a video of this software working on street advertisements: vimeo.com/3464018
See http://theartvertiser.com for more details.
(NB: it appears a little slower than it is due to the fact I'm capturing it to disk using 3d screencapture software).