Clauses like that are really really hard. CC has the NC clause, which is problematic because it may not be clear what consists of commercial use and what doesn't. If a non-profit uses a picture for a fundraiser, is that commercial or not?
The thing that one of the parent comments suggested would actually be quite cool: An alternative license where the "applicants" could ask for permission to use a picture, stating how they will use it. If the author accepts (using a 1-button click), a license will automatically be granted. Everything would still remain free though. And certain use-cases could be allowed automatically (e.g. "personal use" or "use for a non-profit").
It would remove ambiguities (because an explicit permission is granted), but everyting would still remain royalty-free. Plus, the authors would learn how their photos are being used. (I'm happy to give out photos for free, but I'm also happy if people tell me where they're being used.)
The thing that one of the parent comments suggested would actually be quite cool: An alternative license where the "applicants" could ask for permission to use a picture, stating how they will use it. If the author accepts (using a 1-button click), a license will automatically be granted. Everything would still remain free though. And certain use-cases could be allowed automatically (e.g. "personal use" or "use for a non-profit").
It would remove ambiguities (because an explicit permission is granted), but everyting would still remain royalty-free. Plus, the authors would learn how their photos are being used. (I'm happy to give out photos for free, but I'm also happy if people tell me where they're being used.)