Captcha - Recaptcha not appearing in comments

Hi,
I have activated the anti-spam function Google-Recaptcha in the Joomla configuration and also in K2 parameters. But, the Captcha image don't appear at the bottom of the comments section. Only the message inviting you to type the number is appearing.

Could you please tell me if I have made something wrong in the configuration or I have to put somme kind of code somewhere?

Thank you for your answer.

Problem solved!

Don't forget to put also the private and public keys in the advanced tab in k2 section not only into the Captcha-Recaptcha plugin.

Ok, thanks for the info and sharing the solution.