The first RG observation for a taxon gets used automatically to populate the cover photo. After that it is up to users to add or change photos. There are also some old Flickr photos that were used as taxon photos in the early days of the site.
This is a fairly common occurrence, and it would be great if you could document any examples here on this thread, and also vote for this feature request to make such errors easier to detect: https://forum.inaturalist.org/t/flag-or-otherwise-mark-taxon-photos-whose-cid-doesnt-match-taxon/4556/17
Other than that, all we can do for now is correct these errors as we find them, as others have mentioned. Please do this, and don’t be worried about anyone getting offended by it - you are making iNaturalist a more accurate and reliable resource with your expertise!