This is just my guess, but I think the reason why All Might is blurred out is because he's still alive.

And the reason why the other two guys in the back are just silhouettes is because either:
A) Their connection to One for All was somehow cut.
B) Is because Izuku still haven't mastered 100% One for All, so they stay as locked characters.
Or C) All for One gave those two a fate worse then death.

Can we seriously take a moment to talk about the fact that the one user in the bottom left-hand corner looks exactly like Jack Caymen from MadWorld sans the chainsaw hand.