system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does "I'm not a robot" - captcha work?

Would not be a script able to just check the box?
gpt
Those checkboxes are doing more that just observing when you click the box. If it was a script doing so, it would have happened immediately after the page finished loading. So the captcha is watching how long it takes for the box to be checked. Its also watching cursor movements. If the cursor makes a laser straight line or "snaps" to the checkbox control it knows its a script as well. Its looking for an uneven (by computer standards) shakey human looking mouse movement.