This may fall outside of what you're trying to do, but I always thought the best form captcha would be to extend Uber to do real human to human verification. Y

This may fall outside of what you're trying to do, but I always thought the best form captcha would be to extend Uber to do real human to human verification. You send a request to a driver, the driver shows up and confirms the person applying, completing or w/e is actually a person. This can have potential legal/government related application.