Not a bad idea, but some of the questions + pictures I've got have just been plain stupid. One was of a character which I had never seen, let alone know the name of.

"What are these beds called?"

There are about 4 separate names for bunk/cabin beds.

Typos are another issue. "Where do you where these things?" Also, how the hell can you expect people to answer such a vague question?

I have to say that I think this is both harder, and less accessible than a traditional CAPTCHA.