Surprisingly i was facing captcha problem today although it was configured and added the captcha code on contact form properly, it was not showing. Strange! nah? Finally i figured it out – Shy, I was logged in as Admin and browse that contact form!
So, it may happen for many reasons.
1. If you pretty sure you configured it properly, log out and render the template.
2. The code may vary for various form.
* Comment Form
* Photo Gallery Comment Form
* Member Registration Form
* Contact and Tell a Friend Form
Check in which form you are adding the captcha.
3. Enable the captchas related to form. Check the procedures here – http://expressionengine.com/docs/general/captchas.html#comment_form
4. Check if captcha preferences paths are ok from “Admin > Captcha Preferences”
5. Check if captcha files are there