I only tend to think of them when I'm writing on a subject and realise I don't have anything suitable. At the moment, we could use some more options on the theme of education. The other day I wanted something historical, like an old building. Now I'm thinking of writing on the ecotrain QOTW which is the theme of violence in video games, so I guess images around that kind of theme would be good. A few people have requested emotions depicted.
I have got a pinned post in the community where I can add ideas/requests. Not sure if anyone's making use of it, though.