# What is CAPTCHA?

<span class="caps">CAPTCHA</span> stands for \*C\*ompletely \*A\*utomated \*P\*ublic \*T\*uring test to tell \*C\*omputers and \*H\*umans \*A\*part. Basically it means those pictures with wavy letters that you have to type in before being allowed to sign up for a mailing list or other service. They are an attempt to prevent “spamming” or automatic signups by programs. Apparently there are some audio versions as well.

- [http://www.captcha.net/](http://www.captcha.net/)
- [http://en.wikipedia.org/wiki/Captcha](http://en.wikipedia.org/wiki/Captcha)
- [<span class="caps">PHP</span> <span class="caps">CAPTCHA</span> Class](http://www.phpclasses.org/browse/package/3120.html)
- [http://www.codeproject.com/aspnet/CaptchaImage.asp](http://www.codeproject.com/aspnet/CaptchaImage.asp)

[reCAPTCHA](http://recaptcha.net/learnmore.html) is a very intriguing project that uses <span class="caps">CAPTCHA</span> authentication to help correct <span class="caps">OCRA</span> software and digitize books for the internet archive. Fiat Lux!

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**Techniques and Arguments against <span class="caps">CAPTCHA</span>**

- [http://www.cs.sfu.ca/~mori/research/gimpy/](http://www.cs.sfu.ca/~mori/research/gimpy/)
- [http://sam.zoy.org/pwntcha/](http://sam.zoy.org/pwntcha/)
- [Escape from <span class="caps">CAPTCHA</span> Presentation](http://www.w3.org/2004/Talks/0319-csun-m3m/slide1-0.html)
- [Inaccessibility of Visually Oriented Anti-Robot Tests](http://www.w3.org/TR/turingtest/)