Logical Captcha takes advantage of the TextCaptcha.com service, which provides logic-based textual questions instead of distorted images or audio to validate that the entity registering is a real live human being, and not a spam bot. It will provide protection against false registrations and the dreaded spam comments, etc.
An example of such a question might be:
Question: 
Out of a truck, a lion, the color purple, and the number forty-two, which has a door?
Answer: 
truck
Textual logic-based captchas mean that your registration process will be accessible to everyone, including visually/hearing impaired visitors who use access technology to surf the web. It requires a free API key from <a href="http://TextCaptcha.com" rel="nofollow ugc">TextCaptcha.com</a>
This plugin was developed by Josh de Lioncourt of <a href="http://maccessibility.net" rel="nofollow ugc">the Mac-cessibility Network</a>, a site dedicated to blind and visually impaired users of the Mac OS X operating system, the iPhone OS, and other Apple Inc. products and services. Josh de Lioncourt, the Mac-cessibility Network, and related sites are not in anyway affiliated with TextCaptcha.com

Logical Captcha

Integrates a logic captcha to verify that the registrant is a human and not a spam bot instead of using distorted images or audio.

noideaboy

Make the login/registration process on your website simple, beautiful and quick for your website users. This easy to use plugin implements AJAX login and registration on your website. It provides a widget called ‘Ajax Login by WPH’ with which you can setup a beautiful login/registration popup for your website viewers. You can conveniently control its settings including styling and page redirection from the widget screen.
Main Features:
<ol>
<li>Login</li>
<li>Registration</li>
<li>Forgot Password</li>
</ol>
Other Features:
<ul>
<li>Fully translation ready</li>
<li>Beautiful interface with styling control</li>
<li>Optional header image for branding your popups</li>
</ul>

Ajax Login By WPH

Beautiful AJAX login and registration popups for your website.

Logical Captcha vs Ajax Login By WPH