What is a ‘CAPTCHA’?


by Phil Chenevert
Member and instructor for Computer Lab Workshops
Cajun Clickers Computer Club, LA
December 2013 issue, Cajun Clickers Computer News
ccnewsletter (at) cox.net

Have you ever found yourself grinding your teeth because you can't make out those weird words in something like this? All you want to do is get somewhere on the internet to do something and then, Wham! They hit you with this silliness!

Well, they are not there just to annoy us or have fun at our expense. They are there to save everyone a lot of misery so be patient with them. CAPTCHAs, or Completely Automated Public Turing Tests to Tell Computers and Humans Apart, exist to ensure that user input has not been generated by a computer. These peculiar puzzles are commonly used on the Web to protect registration and comment forms from spam.

To understand the need for CAPTCHAs, we should understand spammers' incentives for creating and using automated input systems. For the sake of simplicity, we'll think of spam as any unwarrant

ed interaction or input on a website, whether malicious or for the benefit of the spammer (and that differs from the purpose of the website). Incentives to spam include:

  • Advertising on a massive scale
  • Manipulating online voting systems
  • Destabilizing a critical human equilibrium (i.e. creating an unfair advantage)
  • Vandalizing or destroying the integrity of a website
  • Creating unnatural, unethical links to boost search engine rankings
  • Accessing private information
  • Spreading malicious code


A captcha is a challenge-response test that determines whether a user is human or an automated bot. A typical captcha includes an image of distorted text and a form field for the user to enter the text. Captchas are commonly found at the end of website forms, and must be filled out in order for the form to be submitted. By requiring users to decipher and enter the captcha text, webmasters can prevent automated programs from sending spam or other unwanted data through online forms.

It is estimated that 80% of email is actually spam and captcha’s protect us from most of 'em.  Be patient, use the 'give me another one' symbol that looks like two arrows, or the little speaker symbol to have it pronounce the word if you continually fail to type it correctly. It is kind of like seatbelts, irritating to put on but for our own safety.

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