On Facebook, you have no control when others are sharing your photograph.
The same is true of the Internet in general.
The same is true of the Internet in general.
If you are an entity like the aforementioned NSA, searching the entire Internet for your photo isn't really any more challenging than using Facebook. The computing resources necessary are considerably larger, but that is a relatively small barrier.
If we imagine a more decentralized system, people might well still adopt a single ontology for events and relationships, but much "private" information might actually never be revealed to third parties, as opposed to disclosing all of it to Facebook and asking Facebook to limit whom they show it to.
I agree that it's much easier through facebook, though.