The Captcha Library extension allows you to safely allow anonymous Frontend users to subscribe to events. Install the extension like any typical extension. When you do, the Calendar Base

Illustration 31: The Captcha Field in the Calendar Base Flexform

Flexform will add the Force captcha to subscribe field (see Illustration 31).

Illustration 32: Captcha Extension in the Frontend Display

When you enable the Allow to Subscribe and the Force captcha to subscribe fields, anonymous Frontend users will be permitted to subscribe to events. However, when the do, an obfuscated text string will appear next to an input field (see Illustration 32). The user will have to repeat the string in the form in able to subscribe.