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Captcha
Definition
A captcha is a verification challenge shown to new Telegram group members — such as tapping a button or solving a puzzle — to prove they are human before they can post.
Spam bots can't complete the challenge, so they never get to send messages; members who don't verify within a time limit are removed automatically. This single filter blocks the vast majority of automated spam.
A good captcha takes a real person only a couple of seconds and triggers just once on join, so it barely affects genuine members while stopping bots cold. It's the first layer of any solid moderation setup.
See it in action
Telegram moderation that never sleeps