Since there's no obvious single entity to blame (and even if there is, so what?), we should be working together to prevent and reduce attacks like this. Apart from anything, Facebook popping up a warning about a barcode would go a long way to making people realise that they contain easily readable, and potentially private information.
Also, given how well image classifiers work these days, how hard is it to do the same for photos of (physical) keys, bank cards, and other commonly posted things?
Aren't they already do it for other stuff they don't want to see online ?
Surely a nipple isn't a barcode and legal implication aren't the same. And people sharing personal stuff ARE responsible for sharing those stuff.
So I guess it shows us again that FB is not our friend :)
Do you really believe the problem here is FB? Do you really believe FB should be the arbiter of what incidental information their users's pictures can and can not convey?
And even if they did parse pictures for sensitive data do you believe that FB, given what we know about them would simply redact that information from photos and then discard that sensitive data? I think we can safely assume that FB doesn't discard data on individuals.