@LightBender The functionality is part of the Stack Exchange codebase. There's nothing custom-added by any of the Photo-SE mods. Essentially, it's a feature of the site as much as reputation, voting, questions, and answers. ¯\_(ツ)_/¯
@scottbb Shame, didn't know if they had a plugin library for custom widgets. I don't really know how much customization is actually available for individual communities.