DominicCobb said:

Obviously the only reasonable assumption (and the one everyone makes) is that the ghost is Anakin. But it's an assumption. My point is that Luke wouldn't really recognize his image and that point still stands.

You are the one making the assumption here. You assume people are too stupid to immediately realise who the ghost is. On what basis you make that assumption is beyond me (perhaps yourself?). But when I watched the film for the first time I immediately recognised who the ghost was. And personally I don't know anyone who didn't. So don't make such assumption. I am sure Luke was smart enough to recognise the ghost as well.