Months ago, I saw lots of video examples on blogs and YouTube and finally I got some time and found AS3 sources from some brilliant japanese guys (Libspark).
They built an AS3 library called FLARToolKit which is translated from a Java library (NyARToolkit).
This library can detect a “marker” on a video source and calculate its position in a three-dimensional space.
Theses coordinates can be easily used with Papervision3D and applied on a Collada Object or anything else.

Here is my AS3 Augmented Reality Example, done with a Spongle Bob 3DS file found for free on TurboSquid.

Here are some screenshots :

You wanna test it?

1. Download the marker in the PDF document and print it.
2. Allow Flash to access to your webcam when it asks.
3. Point the webcam at the printed marker.