Suggestion: Tools for Translating Public Domain Comic Books
I think comic books would be particularly interesting for novices and advanced duolinguers, as it would make learning more fun.
I'm certain that a majority of individuals here grew up reading comic books or some form of cartoon.
I'm also aware of the technical difficulties in obtaining text from images and documents of a graphical nature. OCR technology could help to an extent.
But this could be crowdsourced with the right tools, some duolingers could write down the passages in plain text, others could translate, some could proofread, and others could paste it in the bubble.