Depends on D19912. Images currently use `getMock()->getPolicy()` stuff to define policies. This causes bugs with object policies like "Subscribers", since the policy engine tries to evaluate the subscribers //for the image// when the intent is to evaluate the subscribers for the mock.
Move this to ExtendedPolicies to fix the behavior, and give Images sensible policy behavior when they aren't attached to a mock (specifically: only the user who created the image can see it).