CAPTCHA was Google's main method of telling humans and robots apart on the internet, by asking us to enter a distorted code or word depicted on screen.
CAPTCHA's closure is said to be because it no longer provides an accurately way of telling humans and robots apart. Instead, Google has created an invisible version, reCAPTCHA, that monitors user browsing patterns to determine whether they are a human or robot.
After acquiring reCAPTCHA in 2009, Google launched No CAPTCHA in 2014, an "I'm not a robot" checkbox that - if ticked - knows you're not a robot. Google's latest invisible reCAPTCHA removes this box entirely and instead monitors how you interact with websites.