First, to enable Captchas you need the captcha module. Don't get fooled by the documentation stating it requires textimage module. It doesn't. Instead it serves simple, text based captchas. I personally prefer text based captchas over image based, since they are a lot less error prone, and they are accessible to (color)blind people, too. Additionally, as I will explain later on, image based captchas can as easily be bypassed as text based ones, so they don't provide additional security.

Adding Captcha to a web form in Drupal is easy. First, create the web form. Next, get the webform ID. To get the webform ID either use firebug, or stroll through the source code, and grab it. The source  will look something like this:

<form action="/pdxhealingmassage.com/contact" accept-charset="UTF-8" method="post" id="webform-client-form-8" class="webform-client-form" enctype="multipart/form-data" >