You can use captcha security with DJ-Catalog2 "Ask about this product" form.
This tutorial is about core Joomla ReCaptcha functionality; other plugins may work differently and may need a different setup
Here's the short tutorial on how to do it.
You need to generate reCaptcha keys at https://www.google.com/recaptcha/admin#list and obtain both SITE and SECRET keys for your domain.
Now go to System -> Plugins and make sure that the "CAPTCHA- reCAPTCHA" plugin is enabled.
Now enter SITE and SECRET keys into plugin configuration and save the settings.
Navigate to DJ-Catalog2 configuration. In "General settings" tab search for "Captcha" setting and set it to "CAPTCHA - reCAPTCHA". Save the configuration. If your website uses reCaptcha globally, then you can select "Use Default" instead.
Now you can use captcha security with the "Ask about this product" form.
