I should be able to keep my Photos properly private

(User Story, To be Fixed , Priority: Medium, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Photos
Summary: At the moment, photos are purely security-through-obscurity, with long random filenames. That isn't really secure in any meaningful sense. We should be able to set them to be genuinely secure, using Amazon's Secure Token Service.
Note that this should not be entirely automatic, though: I believe that STS will add quite a bit of latency to page loads. Using this should probably be a Property of the Space, and user-controllable.