• The CAPTCHA Project
• The reCAPTCHA project
• Inaccessibility of CAPTCHA: Alternatives to Visual Turing Tests on the Web, a W3C Working Group Note.
• CAPTCHA History from PARC.
• Google Tech Talk on Human Computation
• Luis von Ahn discusses CAPTCHA technology on the PBS show Wired Science, 19 tháng 12 năm 2007. .
• Trang tiếng Việt về CAPTCHA

Defeating CAPTCHAs:

• Breaking a Visual CAPTCHA (Gimpy) By Greg Mori and Jitendra Malik
• Breaking CAPTCHAs without using OCR (talks about a common but easy to fix bug in programming CAPTCHAs, allowing session re-use)
• Defeating a simple CAPTCHA with Open Source software
• Will Solve Captcha for Money? - Article on Slashdot about using low-paid data entry workers to defeat CAPTCHAs in bulk.
• Captcha Exchange Server - Distributed project, defeating captchas from one-click hostings (description in Russian)
• New virus attempts to defeat CAPTCHA with porn - "Virtual Stripper" takes off clothing for each CAPTCHA entered