Shadows and camera tracking

Hello,
I have had some experience in camera tracking and integrating the model into a video feed but I was wondering how do you put realistic shadows for the model into the video.
Thank You

You need to build a mesh that matches the surfaces where shadows will be cast (so you’ll want to track those spots as well). Then you create a “shadow-catcher” material for these new meshes by checking the “shadows only” under the “Shadow” tab of the Material settings. This will create an alpha-ed darkness where shadows ought to be cast. (Be sure to set the material’s “Ambient” setting to 0. Not sure why, but this can make a big difference sometimes.)

Not too long ago, we had a discussion about “shadow passes” that might also be useful for you. The thread is here:
http://blenderartists.org/forum/showthread.php?t=206440&p=1769621
It includes a link to a video that Sebastien Konig made that shows some of the shadow-pass in action. (We were exploring what we felt was a bug, but the discussion might be helpful.)