Another example highlighted here: https://forum.inaturalist.org/t/cover-image-photos-that-appear-to-be-incorrect-or-dont-display-any-feature-to-prove-the-id/33242
Another, perhaps more elegant, way to deal with this might be to identify any observation when its photo gets used as a taxon photo (source_of_taxon_photo=true) and then run a check only for those observations, and only whenever the Community ID of the observation changes. In such an event, that would trigger a process that would flag or mark the relevant photo on the taxon page. I don’t know enough about programming to know whether that would be a more efficient way of doing this.