just FYI. according to iNat staff, photos get downsized if they exceed 2048x2048px. so there’s probably not any reason to load even 6MB if it’s intended only for iNat. probably 2.5MB is the highest you realistically need for iNat.
see https://forum.inaturalist.org/t/enlarging-photo-on-identify-or-observation-page-very-slow/669/20