If the only things on your site are resources for other sites, you could actually make this work using a technology called Subresource Integrity where the hashes live in the link origin (and the browser verifies the content matches the hash on load).

Unfortunately SRI is only deployed for CSS and Javascript (so your collection of JPEGs, or videos, or text snippets aren't eligible unless you somehow wrap them as a Javascript which is horrible) and most sites will themselves be HTTPS so they don't want to have active links (even with SRI) to non-HTTPS sites.