ELI5 CAPTCHA - why can't bots just tick 'I'm not a robot'?

A reCAPTCHA is a CAPTCHA-like system designed to establish that a computer user is human. So how does the reCAPTCHA checkbox i.e. the "I'm not a robot" checkbox actually work? Why can't bots just check 'I am not a robot' and fool the system?   ... We explain like i'm five!   Thank you to the r/explainlikeimfive community, and specifically the following reddit users whose questions and responses formed the basis of this conversation: edshnee, anthonyridad, ekto_, reifenstag, solepsis, nukerx & adipisicing   If you have suggestions, comments, or would like to be a guest on an upcoming episode of this podcast, please reach out to us at [email protected].