Good point Anna. I agree. I think that the award element could also play into the curation. So, when you choose to "download" a photo for use, you'd effectively be upvoting it to pass the author rewards. By doing this, the photos that have more votes would rise to the top.
That said, I do think you'd need to have some other layer of curation. This could possibly be done by having the site owner delegate some STEEM Power to curation experts that'd be able to assist. Also, as a STEEM community owner, you get a "commission", from my understanding. This commission could be used to reward/pay these special curators as well.
I agree, getting "commission" for curation could be interesting!