Text CAPTCHA Logic Questions

A CAPTCHA is a test to tell humans and robots apart. You've probably used one before: identifying a string of letters from an image to show that you are human, rather than a "bot". This site provides a web service to generate textual CAPTCHAs based on simple logic questions.

Which of 81, fifty seven, 60, nineteen, forty five or sixty four is the lowest?

Do you really need a CAPTCHA?

A CAPTCHA is disruptive to the user experience, adding an extra task to the process you want to protect. In the majority of cases, a CAPTCHA is overkill. For example, if you want to protect a comment form from spam there are plenty of tricks to try first.

Do text CAPTCHAs actually work?

Yes, and No.

A text CAPTCHA is more accessible to visually impaired users than their image-based alternatives. To defeat OCR scanning, image CAPTCHAs have to distort the letters used, and they can be tricky to decipher!

The problem with text CAPTCHAs is that they provide inherently more information than a distorted image. They are parseable, under the right conditions solveable. With the advent of contextual parsing tools such as Wolfram Alpha, such simple logic puzzles have become easier to solve programatically.

What is textCAPTCHA?

This site provides a simple web service to generate text-based CAPTCHAs, examples of which are on the demo page. If you wish to use them, find out how the service works, and sign up for your own account.

Questions? Contact Rob.