Add Captcha when Register

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:

Add Captcha when comment