The photos taken for computer vision training aren’t only restricted to the first photo.
It is just the first photo that is used to compare against the trained model (when you click on the suggest an ID section).
All photos should depict the organism. The photos of organisms are included on taxon pages and hopefully there will be a way to view all photos in other areas of the site too: https://forum.inaturalist.org/t/ideas-for-a-revamped-explore-observations-search-page/8439/79
Agree with kiwi that photos that don’t depict the organisms should currently be put in the description, comments section, or in a journal post. iNat isn’t really set up to handle habitat photos, but feel free to submit a feature request! Maybe in an observation field redesign it could have a field type that allows uploading an image.