http://qezqo7c2mvdk2ml2ys626hlh7ezva75wwwoawcuc7xncp37kedumv2ad.onion/index.php/CAPTCHA
Other kinds of challenges, such as those that require understanding the meaning of some text (e.g., a logic puzzle, trivia question, or instructions on how to create a password) can also be used as a CAPTCHA. Again, there is little research into their resistance against countermeasures.