adywan said:.
...the only way to pull this off would be to create a 3d head and track every movement in every shot precisely then mask only the parts that need to be exposed. plus you would also have to match the trajectory of the lightsabre for the lighting on the 3d head.
I made this 3D model a few years ago, Ady. It's in Maya 8.5 but it could easily be converted to any other format.
I too think it would be just too much of a pain to try to match the movement, it's completely crazy to even try, but that's exactly what you've been doing with these movies all along, isn't it? ;) Would it be extremely time consuming? hell yeah! but if you even consider trying it for a second, my 3D model is yours in a heartbit.
But if anyone here wants to have a go at it, I'll gladly send the file as well.

Here you can see more pics of the 3D helmet:
http://afohusker.deviantart.com/gallery/
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Now, let me thank you for all the work, effort and love you've put into making these films what they should've been a long time ago. I've been reading this thread since it started, right after I stumbled upon ANH:R and WOW!
To be honest I had lost my love for SW... with the prequels and all, but now I fell like a little kid again when I watch ANH:R and that's just because of what you've achieved.
I never felt like I could really contribute with anything so I was just lurking, reading endless debates about flippers and snow flakes, green lasers and whatnot, but all in good fun. Ah! and blue TIEs LOL!....but reading that the only chance to achieve a certain VFX needed a 3D Vader head, made me finally create an account, just in case one day you find good use to it. If not, well at least it helped me make the jump into this amazing project.
Thanks again, man, and keep surprising us!
:D