In the context of a forum for a school (one category per class), this plugin is quite interesting !
We can post pictures, add comments and have a nice overview.
Particularly useful would be this pull request: Add sitewide and category gallery scopes - Pull Request #23 - Canapin/discourse-topic-gallery - GitHub
Indeed the use case would be opening topics per events and posting pictures related to an event in a dedicated topic.
And with the sitewide and category gallery scopes people can have a nice overview of all pictures without having to go into each topic !