What is a CAPTCHA?

Sherry Holetzky

Obviously, CAPTCHA is an acronym. The question is what does it stand for? The answer is fairly simple, as is CAPTCHA's purpose. A CAPTCHA, or Completely Automated Public Turing-test to tell Computers and Humans Apart, is used to keep bots and other automated programs from signing up for offers, collecting or signing up for email addresses, violating privacy, trying to crack passwords, or sending out spam to unsuspecting email recipients. A CAPTCHA works by issuing a challenge to the person or entity attempting to gain access.

One use of a CAPTCHA is to prevent bots from trying to crack passwords.
One use of a CAPTCHA is to prevent bots from trying to crack passwords.

A CAPTCHA challenge is usually a simple visual test or puzzle that a sighted human can complete without much difficulty, but that an automated program cannot understand. The test usually consists of letters, numbers or other images that overlap or intersect. The images are distorted in some way or shown against an intricate background to keep them from being easily read by another computer.

Gimpy is one example. Gimpy is a type of CAPTCHA that chooses short, random words from a dictionary and creates seven puzzles like those described above from the words. The user must then guess at least three of these words correctly in order to proceed. Pix is another interesting example, and as the name indicates, it uses pictures to create a challenge. This system provides six pictures on the same topic and requires the user to determine the subject matter.

Unfortunately, CAPTCHA technology runs into some problems. A sight-impaired individual will not be able to respond to the challenge without help. There is also the issue of relentless spammers and others that hope to take advantage of the online community who continue to develop sophisticated programs to decipher CAPTCHA images. Even though CAPTCHA technology is updated consistently, problems may still exist, especially when the images must become more and more skewed in order to fool bots. Some CAPTCHA images are even difficult for humans to interpret and may turn away legitimate clients or customers.

Despite the obvious problems, CAPTCHA works fairly well in many settings. It keeps untold numbers of bots from signing up for thousands of email addresses every day that would be used to send out spam. It is an excellent tool, but continuing to improve on it will require dedicated people and meticulous attention to detail in order to keep up with spammer's new tricks.

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