Suggestion: we could upload images ourselves.
There is already a webpage for each word we learn. It would be awesome if we had a kind of image uploading and voting system for the users, like the guys at Memrise do.
No, because the pictures that Memrize filled up with were mostly fatuous nonsense and pictures of women scantily dressed. Which is ok, but not helpful. I like that this site is so far low on nonsense. If you want to use mnemonics, then that is great, but please don't try to inflict them on other people.
Yes, it is mostly nonsense, that why they are so memorable. There is a gread TED talk of Joshua Foer about that subject (and the book is awesome). And Idriz Zogaj at TEDxGoteborg explains about hia simliar experience.
But i believe that your worries are legitimate. However that problem could be solved by a "flag it" button. Or just voting as "not helpfull".
The fact is that Duolingo already uses images. They just are in a insufficient number for now.