Currently there are only three options for photo uploads: Photos you took yourself, Creative Commons, and Public Domain. I suggest that there should be a fourth option: used with permission. Say a friend has taken a trip and found a cool thing that you both agree should be added to the Atlas. However, he doesn’t feel like writing a place article, and doesn’t even have an account. Your friend suggests that you write the article, using his photos. It would be awkward to claim credit for photos you didn’t take, even if you had permission to use them.
The CC and Public Domain options already have attribution fields. It seems as though it would be simple to have a mandatory Attribution field on this category of photo, and possibly even an “explain how you got permission” field to discourage theft. It could even help simplify some cases of co-authorship, when one author is writing most of a piece and another is providing the photos.