atitan

Math Quiz generates dynamic math problem in the comment form to beat spam robots and supports flexible form style customization.
Demo website: https://atifans.net/ (with Supercache and AJAX comment form enabled)
For PayPal donation, please use this email address: info a.t atifans.net
Features:
<ul>
<li>Dynamic problems prevent spam robots from posting unwanted content.</li>
<li>Quiz form inserted using AJAX for better compatibility with HTML cache plugins.</li>
<li>Form style and position can be customized in the control panel.</li>
<li>Trackbacks and Pingbacks are checked with DNS queries to avoid abuse.</li>
<li>Optional login page protection.</li>
</ul>
Translators:
<ul>
<li>SLV-es (Spanish)</li>
<li>Joao Paulo (Portuguese)</li>
</ul>

Math Quiz

Math Quiz generates dynamic math problem in the comment form to beat spam robots.

Todd Nestor

Hercules Recaptcha uses the latest Google Recaptcha API to more accurately determine if users are bots or not. 
If the user is not logged in it will display a Recaptcha for the user to fill out in the comment form. If the user 
disables javascript and is not logged in then comments will fail to submit.
The Recaptcha is also added to the registration page for both multisite setups and single blogs. There are options for 
having it show up on comments and/or the registration page, as well as options for its position on the comment form, and 
which style (Google gives only two options, dark or light).

Hercules Recaptcha

Hercules Recaptcha adds a Recaptcha to the comment form for non-logged in users.  It uses the latest Recaptcha API.

Math Quiz vs Hercules Recaptcha