Smartor Photo Album (which isn't a full album app, but just phpbb mod-add-on) has such a feature. Flickr does of course. Gallery offers it as a module. It might be nice to add such a feature to future versions? I was under the impression that coming from Smartor, which is a free small add-on, that Photopost would have such a simple feature being that it's on version 5.14 now.