I'm brand new to blender but I have an upcoming project that might be a perfect fit. I need to take a short movie, define a region in the movie which needs to be tracked. Once that it done this will become a template. I then want to be able to insert a picture into the movie at the predefined motion tracked area. The end effect is something like a commercial with someone holding a tablet and you are simulating the picture displayed on the screen.

Now the hard part is that I want to automate this process because the picture can change I need to regenerate the modified movie whenever the picture changes.

Is this possible and if so can this be done on some low end hardware if the movie clip is only a few seconds long?

so there is one movie clip to be tracked and you wanna have different images linked to the tracked path?
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I'm sitting, waiting, wishing, building Blender in superstition...

No, actually there will 1 image file (capture from a web cam) that will need to be inserted into the movie clip

you can't automate (planar) tracking in your case. But once tracked, you can hook anything to the tracker markers. If you want two separate rendered videoclips with your movie shot and different pictures in the tracked area, then you need to change the image an re-render.
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I'm sitting, waiting, wishing, building Blender in superstition...