I recently discovered two new logical-based captchas plugins for WordPress.
1. Logical Captcha (Version 1.0.3, Updated 2009-8-24) 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. [Logical Captcha was last updated 11 years ago as of 2020. Tested up to WordPress 2.8.4]
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 TextCaptcha.com
This plugin was developed by Josh de Lioncourt of the Mac-cessibility Network, 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
2. Accessible Captcha 0.1. The Accessible CAPTCHA asks users random questions from a database of very simple questions. The questions contain markup that allows the system to randomize how the questions are asked. It is easy to add new questions and, with a little PHP skill, add new types of questions. Try the demo at https://linkleaf.com/acaptcha/acaptcha.php is No longer available to download from WordPress. This plugin allowed you to customize the questions by editing the questions.txt file.
This plugin was created by Carl Zulauf, a 25 year old Computer Programmer residing in Omaha, NE. Carl created his blog because "Sometimes you just have to publish things yourself…"