VIMP offers reCaptcha as an alternative captcha in the registration form to protect you from spam.
In order to use the reCaptcha plugin, please register your site
at https://www.google.com/recaptcha/admin/create first.
With entering your domain name the required keys will be created.
Next, enter both public key and private key at Configuration -> reCaptcha within the VIMP backend.
Finally, select library "stReCaptchaPlugin" at Configuration -> Captcha in order to activate reCaptcha.