I believe reCAPTCHA's true purpose is to harvest user information and labor from websites.

C’est un fait, les CAPTCHAs existent uniquement pour nous faire travailler gratuitement. Ils ne servent pas à protéger les sites des robots, ces derniers résolvent les CAPTCHAs mieux que nous.

As the paper points out, image-labeling challenges have been around since 2004 and by 2010 there were attacks that could beat them 100 percent of the time.