Here is another way you can look at this:
When people disguise as other people they put on their face a mask that has variations in depth. Some people have bigger noses, others holes in their cheeks... and so on. If you put that mask on a table, just like you would unwrap a head you will get a plane that has bumps and holes in it. If you take a picture from above with shadows in the holes and highlights on the bumps and then desaturate it you will have a bump map. The bump map isn't a normal map but it is exacly the same thing. All you need is the nVidia plugin
I don't know how to say this better. At first I didn't understood as well... but after testing a lot of things I got it.
Hope you figure this out to. I hope this helps... If you still have questions post them here. I'll be happy to help again. And who knows... maybe someone else can put this better then I can
