Add the new, simplified Recaptcha2 ("I am not a robot"-checkbox) to your register and edit-forms. Based on the recaptcha-plugin by Adrian Schlegel. This plugin is not very actively maintained and is available for adoption.
Compatible with DokuWiki
Hrun, Detritus
reCAPTCHA provides a CAPTCHA with text from scanned books and images. This new version of recaptcha protects your registration form and edit forms from spammers, while posing a minimal hurdle for humans. For more information see http://www.google.com/recaptcha.
To use the reCAPTCHA service you need a Google account and create an API key at https://www.google.com/recaptcha/admin