At OpenStreetMap we would love a map-based CAPTCHA that actually contributes to our map. Right now we (like most people) use ReCAPTCHA on our wiki... which has

At OpenStreetMap we would love a map-based CAPTCHA that actually contributes to our map. Right now we (like most people) use ReCAPTCHA on our wiki... which has the rather exasperating effect of contributing map data (StreetView house numbers) to our main competitor, Google. On the upside, you can usually type a wrong number into the ReCAPTCHA. ;)