> most ad-blockers don't actually block ads; they just block cross-domain, spying widgets. Nothing is preventing you from showing a self-hosted, untracked image that's actually an ad.

Most ad-blockers I know of use cosmetic filters, which can hide any element from a page, including self-hosted and non-tracking ads (see https://www.troyhunt.com/ad-blockers-are-part-of-the-problem...). Sadly, showing ads that are respectful to the user is not that easy...