In my photography courses, we use Flickr to upload photos to a group pool which is run by our teacher. There we can see each other's photos, leave feedback and see what our classmates are doing on different assignments and personal work outside of class. The community feeling in Flickr really is great for those interested in photography because it offers a wide variety of subjects and photographers ranging from amateur to highly experienced professionals. You can set your content filters to exclude violent content or nudity, and if a user's photo falls outside your content filters, Flickr will warn you. It's a good site, all in all.

This is a really good website. It's less inappropriate than things like deviantArt. Although there is some violent and sexual content, I think it's actually pretty rare. There's some really breathtaking pictures, too. The community is pretty friendly overall and I haven't come across any trolls so far. However, judging by some of the reviews below, there are some. There's trolls on everything, so it's really nothing new. You just got to learn to ignore them and if someone hates your stuff, ignore them, too. All-in-all, it's really good.