Came here to add this feature suggestion and (fortunately) discovered that it had already been proposed. It’s great that iNat has taxon photos, and I do understand that earlier in the project’s evolution there was a need to find photos for a whole lot of taxa when there weren’t yet a lot of well-curated RG observations. This resulted in taxon images being added based on observations whose community ID is now not a match. Similarly, a lot of images were added from Flickr (and to a lesser extent EOL and Wikimedia Commons).
It would be wrong to automatically purge any “misfit” images, but it would be great to highlight them. As suggested by @jeanphilippeb and @suecar, a red bounding box or exclamation mark would seem appropriate, maybe with a popup note along the lines of this:
Although this image was chosen to illustrate the species Eleustrine latifolia, the observation it was taken from currently has a community ID of Cobana campanulata. You may want to consider replacing this image with one from a Research Grade iNaturalist observation of Eleustrine latifolia.
Given that the need for off-domain image sources is now much reduced, I think it would also be appropriate to have a similar yellow warning for non-iNat sourced images:
This image was chosen from [Flickr/EOL/Wikimedia Commons] to illustrate the species Eleustrine latifolia. We can’t be sure whether the image creator applied the correct identification and you may want to consider replacing this image with one from a Research Grade iNaturalist observation of this species.