Hello!
We suggest you write a plugin that implements the functionality:
On the user side would be to count the pages perhodov (entry in cookie).
When you go to the 10th page, you perebosit on a separate page,
We derive pop up prompting you to enter a captcha (image will be generated from a random number), if the CAPTCHA is entered correctly, you will redirect to the page you were before ktoroy, if captcha is incorrect, you stay on this page, get a new captcha.