A good setup is to use ARToolKit plus osgART.
The tutorial of ARToolKit also explains also some of the principles of Computer Vision:
http://www.hitl.washington.edu/artoolkit/documentation/
osgART is the ARToolKit for OpenSceneGraph and abstracts some of the principles of using a computer vision based tracking in a scenegraph application
Both toolkits have a large and vibrant development community.