It occurs to me there are tens or hundreds of thousands of images donated en masse (GLAM etc.) that are only categorized as "image from X collection" or "Files donated by X", i.e. essentially uncategorized by content. 

This obviously greatly reduces the likelihood of discoverability and re-use.  But it's hard to find such files, and the massive categories (thousands of files, often) don't make organizing the work easy.

I'm think of a gamified interface -- à la Wikidata Game -- that would let a volunteer (after OAuth identification) pick a category (from a pre-fed list of massive categories of donated files) and show one photo from the category that has only that category listed (i.e. has no categorization by content), and let the volunteer type (with auto-complete, like HotCat) some appropriate categories and hit Save, and the categories would be added, and the next file shown.

(Optionally, a second layer of verification could be added, where volunteers would [also] be invited to vet or change previous volunteers' categorization, and actual change to categories on Commons would only take place after 2 (or N) users approved the categories.  I'm not at all sure this is needed, and I think we can start without it and see how it goes.)

So, does something like this exist?  If not, who wants to build it? :)

   A.