That little background image feature in CSS has given up quite a bit of data in similar situations (people used to use it to check browsing history of :visited links before browser started blocking that).
It's intended to ensure that a CDN doesn't change the content they're serving to your users.
But it turns out you can approximate the speed a visiting browser computes those hashes to fingerprint browsers just by including some CSS on a page.
They use SHA512 which is fast, but noticeable for large enough files.
Yes, the point is that it works with blockers.