Follow the next steps in order to install and configure Captcha plugin for your WordPress website (for standard registration, login and comments form only).
- Install and activate the Captcha plugin.
- Navigate to Captcha > Settings page.
- Set necessary parameters on the plugin settings page and save changes.
Captcha is displayed only in case you're using standard pages for registration, login and comments form. It seems that your Wordpress theme uses custom forms.
If you activated captcha, but it is not displayed in the form and doesn't allow you to leave comments/register either ("empty captcha" error) it means that this functionality is not supported by your theme (plugin).