Tagging or marking directly on photo has been a feature in several buddypress photo plug ins from the very beginning. Lack of this makes BP Media plugin somewhat unusable as-is just now. This feature has been planned in distant release but this is really urgently needed. Thanks.
We plan to provide tagging feature as premium addon. We are waiting for BuddyPress 1.7 after which UI related things features will have lesser chance of breaking.
We will update project roadmap soon.