/3/ - 3DCG

Don't wanna make a seperate thread for this:
In blender, when using motion tracking, how do I anchor 3D objects to tracking points within the scene, so that everytime the anchors move, the object moves as well?

Also, while I'm here: why does my footage when using it in this composite ALWAYS come out overexposed? I don't have a lightsource in my scene and I have not fiddled with looks or curves or exposure.
I tried fiddling with gamma and curves to counteract, but nothing helps. Adding a light source only brightens the image (a bit)