You must be hard of seeing.
I'm an artist, actually, and I have to make visual comparisons all the time.
Have you not noticed yet that the ears in the picture you posted are a good bit SMALLER than the ears in the tabloid picture? You could put part of that down to perspective or camera distortion, but still.
His forehead is covered by something. Forehead shape is another way we identify others.
And his mouth's stuck inside the bong, so we can't rely on THAT feature either.
It may very well be Michael Phelps, but there's nothing in this photo that screams "Michael Phelps!" definitively. In fact, that picture looks a lot more like one of my college boyfriends than it does Michael Phelps.