This is an excellent summary and synthesis of previously disconnected ideas. I was able to remove several votes on other feature requests to free up enough to add one to this feature request.
Yet another relevant topic:
https://forum.inaturalist.org/t/duplicate-prevention-notify-observers-if-their-image-checksums-match-others-on-the-site/258/8
Minor quibble: I would swap the threshold times for #3 and #4.