tracking to create information for an object?

Hi,

I’m using tracking, but now I think what this is doing is tracking to create a background movement. What I need to do is track an object so that I can replace it in a scene. Are there tutorials for this type of approach? I also have several instances where my object goes behind something, or goes offscreen. Is there anything in addition to this that shows how I can run a tracker offscreen?

Thanks
Dave