Captcha for Member signup Protected Content

We're using Protected Content and have two membership levels. One is a Basic Free membership which is available for signup from the front-end.

When a user encounters a page/content that requires signup - they can either sign-in with an existing account or create a new account for the Basic Free member level.

My concern is that we may get spammy signups. Has anyone integrated a CAPTCHA into the auto generated account signup form that PC automatically creates?

Any ideas as to how to achieve this?

Thanks in advance.

-Jeff