The glaring hole in this story is: how are they going to *know* which images "contain nudity"? It's all very well to say they'll blur those, but that's cart before horse.
Could as well say "we'll make our social network safe by banning all the bad people," which in fact they are also saying, and we know how well that always works.
Very likely, the purported answer is going to be two letters long, and that is not an adequate answer for obvious reasons.