Setup CAPTCHA in Content Types
Please check README.txt of the captcha module.


  The configuration page is at admin/config/people/captcha,
  where you can configure the CAPTCHA
  module   and enable challenges for the desired forms.   You can also
  tweak the image CAPTCHA to your liking.  



Go to the configuration page - admin/config/people/captcha  
Select the Default challenge type - Math or Image  
In the form list, you can define which form has CAPTCHA, for example
if you want to have it on the register form, select a challenge type
(Math or Image) for the FORM_ID user_register_form


If you want to add CAPTCHA to a content type, for example, blog, add a new FORM_ID "blog_node_form" and click "Save Configuration".

By default, you will not see CAPTCHA on each form when you logged in as administrator, but you can change the option in the configuration page.