Is it possible to protect content types with captcha? I would like to protect some pages of my Drupal 7 website with a riddler captcha, to protect those pages from all who can not solve the riddle, but don't make it necessary to login to see the content. As I am using Organic Groups it would be the best, to protect all content that is part of a group by such a riddle.
To make my goals more clear and avoid misunderstandings:


I want to protect pages in a soft way against unauthorized access.
I don't want the audience to login to my side, because for my use case that would be too complicated.
I don't need high security.


Does anybody know how to do that, what would be the most elegant way. Does anybody have a better idea?
you may create custom module
https://stackoverflow.com/questions/3434134/restrict-node-with-captcha

combine hook_node_view_alter with
http://drupalcontrib.org/api/drupal/contributions!captcha!captcha_api.txt/7