You can add a title and description to images, folders, albums (what we've been calling folders), sub-albums, etc. You can search on those, but it's not a structured thing like tags. I guess you could just store some JSON in there but you might need to get smart with your queries to search. Afraid I have no idea if there's plugins, or even if what I've been using is a recent and/or unmodified codebase.

I think it's more designed for photo uploads, as there's an option to keep exif data, and it automatically makes images of different sizes (including your original, maybe massive upload).