Add Captcha for Registration

Log in as Administrator, click the  button to open the drawer menu, then click on "Administer Wiki":

In the wiki administration page, click on the "Registration" link from the vertical menu to the left.

Next, scroll down through the options. Find and pick option REQUIRE CAPTCHA TO REGISTER:

Then, in the wiki administration page, click on the "Rights" link from the vertical menu to the left.

Next, click on the radio button "Users" to display the access rights for Unregistered users and give them View and Register right:

To see the result of these settings, logout and click the  button to open the drawer menu, then click on "Register":

Now you camn add the details in the registration form, including Captcha:

Add Captcha for comments

Log in as Administrator, click the  button to open the drawer menu, then click on "Administer Wiki":

In the wiki administration page, click on the "Rights" link from the vertical menu to the left.

Next, click on the radio button "Users" to display the access rights for Unregistered users and give them View and Comment right:

Then, pick the option Require unregistered users to solve a captcha when posting a comment on a page:

Finally, logout and check the result: