Google’s reCAPTCHA system requires users to press and hold the “I’m not a bot” button on a challenge page, such as this one. The reference ID provided is linked to the user’s interaction with the reCAPTCHA system. This technology helps protect websites from automated programmatic (bot) traffic. By verifying that a user is human, reCAPTCHA ensures that legitimate users can access website content while bots are blocked.
Source: https://www.sfchronicle.com/entertainment/article/jeff-bezos-mother-dies-20819051.php