Technically it's possible to have an index of all images published is some registered media and assume they are already vetted by editors of that media. Then you compare the published picture and voila - you do not have this problem at all. Of course, it adds some costs, but it's exactly what M.Zuckerberg can decide to spend money on (before delivering this service to people in Africa and other places where it's easy to abuse Facebook censor mechanisms - ask Russian opposition how Putin's media warriors take down their posts).
I think that it’s much more safe to prohibit all nudity than nitpicking what to allow and what not. There are TBs of pictures uploaded daily on Facebook, it’s not a trivial task.
What's wrong with this image? Of course it should be allowed. I see no difference with David by Michelangelo, for example. Banning all nudity is just stupid censorship that has no moral ground.
I believe that a lot of conservative people would find a picture like that offensive. We have to keep in mind that Facebook's audience is in the billions.
It's not the reason for censorship. Facebook may offer parental control and display explicit content warnings to serve this audience. After all, people who find nudity offensive may limit their subscriptions to accounts which do not post it - it's not that they are forced to look at it.
