system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: if captcha codes/puzzles are being trained by us humans to recognize stairs, bikes, taxis, etc, how do they know when we're mistaken?

For example i have a set of 9 images from which i am supposed to select the ones containing bridges or traffic lights. If i dont select them all, it wont let me pass. How does it know if we're training them by completing?
gpt
By receiving results from thousands of users, statistical models are used to separate real from fake users by looking at the grouping of data. Fun fact: data collected from certain captcha were actually used to train algorithms to read blurry text. By giving two tasks to the user, the first verified the user to be human and the second was used to train computer to be better at reading.