Surely the spare word allows the dictionary of potential CAPTCHA words to add a new word for every CAPTCHA solved (sure they probably run them past many users for validation purposes). This effectively allows the CAPTCHA service&#x27;s dictionary to scale&#x2F;evolve continuously, preventing an anti-CAPTCHA service from &#x27;learning&#x27; the whole dictionary.<p>I thought this was the entire point of re-captcha, so regardless of the &#x27;time necessary to complete&#x27; element, their case doesn&#x27;t seem very well thought out.