> The actual screenshot isn’t sent, some hash is generated from the screenshot and compared against a library of known screenshots of ads/shows/etc for similarity.

this is most likely the case, although there's nothing stopping them from uploading the original 4K screengrab in cases where there's no match to something in their database which would allow them to manually ID the content and add a hash or just scrape it for whatever info they can add to your dossier.