system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How exactly do CAPCHAs work? If a bot wouldn't be able to fill out a capcha correctly, how are computer programs able to tell if I answer correctly?
gpt
The program generating the CAPTCHA knows what it is because it generates it. It isn't a static image just stored on a hard-drive, they are generated dynamically by taking a sequence of letters/numbers and then distorting them. The computer knows what those letters/numbers are *before* it distorts them, so it knows what the correct answer is already.