Updated Inaccessibility of CAPTCHA Note Published

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Today the Accessible Platform Architectures (APA) Working Group, with the assistance of its Research Questions Task Force (RQTF), has published "Inaccessibility of CAPTCHA," as a Working Group Note:


First published in 2005, today’s 2.0 publication extensively updates the earlier version to bring our analysis and recommendations up to date with CAPTCHA practice today.

CAPTCHA technologies covered in today’s publication include:

  • Traditional visual and audio CAPTCHA, including CAPTCHA games and logic puzzles as practiced today,
  • reCAPTCHA v2 and v3,
  • Blinded verification tokens,
  • Honeypots,
  • Biometrics,
  • Proof of Work,
  • Heuristics, PKI certificates, and much more.

Today’s publication is the culmination of almost two years of extensive research, discussion, writing, and editing by RQTF. The document is extensively documented with references to research publications and numerous on line resources. Comments received in response to three separate wide public review draft publications aided our work immensely.

We thank the community for your invaluable input over the past two years. Your comments have helped us improve our analysis of the state of the art in telling human users apart from their robotic impersonators. Your comments have significantly aided our work on this updated Note. We truly could not have done this without your help.

While today’s publication closes our current work on the topic of the inaccessibility of CAPTCHA, future updates are certainly likely. Therefore we continue to welcome comments and suggestions.

To comment, please file an issue in the W3C apa GitHub repository. If this is not feasible, please send email to public-apa@w3.org (comment archive).

Janina Sajka, Chair Accessible Platform Architectures (APA) Working Group

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