@pluralistic @alttexthalloffame @Gargron @AltTextHealthCheck the EXIF 2.1 and 2.2 metadata standards include attributes for both ImageDescription and Copyright. The definition for the latter identifies it as "copyright holder" but it could be used for broader license information.
@lukethelibrarian @pluralistic @Gargron @AltTextHealthCheck Great! We'd then just need Mastodon (and the rest of the fediverse platforms) to allow editing and displaying this information, without having to change the ActivityPub standard.