Just looking at it, my first instinct would be to say the guy was photo-shopped in, but given the circumstances under which it was taken and sent, I don't see how he could have done it without leaving any traces (trying to do photoshopping on a phone with your finger while on a bumpy bus ride would be a unique and impressive feat by itself).
As always, I'm not saying that this is a real ghost - I can think of a few possible explanations (though they may not be the RIGHT explanation). It's a pretty cool shot either way, and kids go nuts when I tell them about it - the "man in a black suit with no face" thing is a description of Slenderman, a ghost story that every kid seems to know about these days.
What do YOU think?
Update: a security guard who works in one of the buildings opening to the alley is fairly sure it's him in the picture. But the guard in question has a beard, so...
Of all the stops on my tours over the years, this is the one I've used most frequently. I have several routes that I switch back and forth between, and a repertoire of plenty of different stops. But this one has been on every route - I can't think of any period when I was skipping it.