Ron Nazarov@signaleleven @datenschutzratgeber @threemaapp The specification has reCAPTCHA as an authentication method (https://matrix.org/docs/spec/client_server/r0.6.1#google-recaptcha), and the Synapse README.rst recommends using reCAPTCHA for open-registration servers (https://github.com/matrix-org/synapse#readme): "By default, registration of new users via Matrix clients is disabled. To enable it, specify enable_registration: true in homeserver.yaml. (It is then recommended to also set up CAPTCHA - see docs/CAPTCHA_SETUP.md.)".
@signaleleven @datenschutzratgeber @threemaapp It could mean another CAPTCHA, but the only CAPTCHA supported is reCAPTCHA (https://github.com/matrix-org/synapse/blob/develop/docs/CAPTCHA_SETUP.md): "The captcha mechanism used is Google's ReCaptcha."
