A couple notes about Creative Commons:
First, could the observations filter for CC license include pictures with licenses that are strictly more permissive than the one selected? It's silly to have to click through up to 7 options to find all the pictures that may meet your criteria.
Secondly, have you looked into what it would take for iNaturalist photos to show up on Google Images search when "usage rights" is included in the search? For perspective, a search for pictures of the fly
Spilomyia fusca with any CC license yields:
- 1 picture on Google Images
- 4 pictures on Flickr
- 50+ pictures on iNaturalist
Right now, nobody is really likely to find these photos unless they already use iNaturalist. If it's possible, you could vastly increase the number of photos of organisms available to the general population, and as a bonus likely attract more visitors to the site.
Reuven