The Join Captcha Bot

The Join Captcha Bot verifies incoming group users are real humans through an image-based or math captcha before they can send messages. It is open-source and translated into a large number of languages, which makes it a solid pick for international communities rather than Russian-first tools like Captcha_Rubot.

It also supports restricting new members from sending media, links or forwards for a grace period even after they pass the captcha, adding a second layer against accounts that get through verification but are still spam bots. Configuration happens through in-chat commands rather than a web dashboard.