Google acquired reCAPTCHA in 2009. It's one of several services that help distinguish bots from real people when signing up for say e-mail accounts. It presents garbled, fuzzy or other hard to decipher text with the idea that humans are far better than machines at decoding it.
Google explained to TechCrunch it is now including house numbers, street signs and other graphics from Street View in reCAPTCHA as a to test if its a good way to get "double duty" from its purchase.
I recall this sort of work being done via Amazon's Mechanical Turk in years past.