Almost 100% definitely from maps. The real value of CAPTCHAs is in crowd-sourcing identification work (watch the TED talk if you haven't already).
I know of a case where a company paid to have scraps of illegible handwriting shown in CAPTCHAs so that hundreds/thousands of people would look at them and try to decipher.
Newer CAPTCHAs are helping to train AI for self-driving (see relevant xkcd of course). Asking people to interpret actual street views and comparing to the computer's interpretation is exactly how the tech gets better.