What are CAPTCHAs?

CAPTCHA is an acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart".

That's the theory.

In practice, CAPTCHAs are used primarily in social networking features (adding friends, writing messages, etc.) comment functions, downloads, blogs, forums, guest books and in registration. In short, they’re used everywhere in the design of the Web's interactive activities. The differentiation between man and computer is necessary to protect websites, forums and blogs from so-called spam-bots–spam programs that tag websites with prohibited statements or unpaid advertising, or even read your private data. CAPTCHAs help to verify whether the user is a "real" person or a machine. It’s done by means of distorted strings of mathematical tasks. To decrypt them the user must solve one of these tasks to identify as person.

However, as the spam tools continue to get better, conventional CAPTCHAs no longer provide sufficient protection against bots. The result? CAPTCHAs are getting increasingly complex, and thus, at least for real users, increasingly difficult to decipher or solve–especially for disabled visitors with reading, learning or physical disabilities. For the average user, meanwhile, solving a CAPTCHA is still an increasingly difficult task.

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Stand: 29.02.2012, PDF-Format, 675KByte