After thinking this through, it's not as simple as I thought, sorry.

I said earlier that we are doing this already for article-level image recommendations; that was wrong. We only have somewhat similar logic for link recommendations (via the SearchDataForIndex2 hook handler), but there 1) we can rely on our local recommendations cache to do certain checks, 2) running out of recommendations isn't really a concern since we can generate them quickly and frequently. So that solution is not applicable here.

The thing is, there are very few places in MediaWiki where you can efficiently decide whether an image got added; and for section-level images we need to differentiate an edit adding an image to the article from an edit to an article that had images (but the edit didn't touch them). There are several hooks with access to the ParserOutput (which tells what images are present in a given version of the page), and some hooks which give access to both the old and new version of the page (so the old and new ParserOutput could be generated; but that's an expensive operation, and these hooks are called during save and are performance-sensitive); but there isn't any hook that readily provides access to the old and new ParserOutput (or equivalent information).

The closest thing is LinksUpdate, which provides a before/after view of internal and external links, but not images. It would probably not be too hard to add, but obviously that's not something to attempt while the MVP isn't finished.

Moving to maintenance as it appears we may want to attempt this at some point