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Difference between CAPTCHA and Re-CAPTCHA

One of the most useful devices to have been developed for the web is CAPTCHA. If you have surfed to any website that requires you to type in a visually obscured word for purposes of verification, then you have already seen CAPTCHA at work. As for reCAPTCHA, it is a closely related technology that in some ways may be seen as the opposite of Captcha, and in other ways as its other aspect, as this comparison article will show you.


The Basics

A CAPTCHA is a challenge-response test that is commonly used on the Internet as a way to ensure that the respondent to a query is an actual human and not a computer. During the test, a server computer sends out a word that is distorted and/or obscured (either intentionally or by virtue of poor quality scanning) so that another computer cannot decipher it. A human can decipher it however, and in doing so, the server determines that it is in fact a human that has entered the word. With reCAPTCHA, CAPTCHA itself is used to digitize textbooks as well as protect certain websites from unauthorized entry by bots. This also has another equally important use in digitizing text that would otherwise be impossible to scan into a computer via OCR or optical character recognition technology.


The term “CAPTCHA” is derived from the word "capture", and it was introduced by a group of Carnegie Mellon researchers that included Luis von Ahn, who would later develop reCAPTCHA. The CAPTCHA acronym stands for "Completely Automated Public Turing test to tell Computers and Humans Apart." Early on, attempts were made to trademark the term, but they have since been discontinued. As for reCAPTCHA, the program is the brainchild of a computer scientist from Guatemala named Luis von Ahn, who was also involved in the development of CAPTCHA. With the help of funds from a MacArthur Fellowship, von Ahn’s developed a counterpart to CAPTCHA that took advantage of a resource that he felt the earlier system squandered needlessly: human brain cycles. von Ahn realized that the human effort required to decipher and then input the obscured words used in the CAPTCHA system could be put to better use by digitizing words that aren't legible via OCR .

In Use

CAPTCHAs are typically used found to prevent automated blog or forum posts. This has been proven an effective way to prevent commercial promotion and vandalism on the Internet. ReCAPTCHA for its part uses the same technology in order to digitize scanned text from subscribing sites. In essence, each and every time someone reads and types in the obscured word in a CAPTCHA, he or she is actually contributing to the digitization of scanned manuscript whether or not he or she is aware of it.



  • Used to prevent the unauthorized posting of bots on the Internet
  • Effectively curtails spam and promotional attempts
  • Is a key component to reCAPTCHA technology


  • Relies on CAPTCHA to provide deciphered words for subscriber sites
  • Utilizes human brain cycles which would otherwise be wasted
  • Was invented by Luis von Ahn, who was also one of the developers of CAPTCHA


comments 1 Comments

  • Paul . 3+ yrs. ago

Text-based Authentication is a thing of the past and still continues to be a problem for most people along with it still allowing for SPAM/BOTS to get through you have to now contend with Phish Attacks. Anyone that has ever used CAPTCHA and/or RECAPTCHA know that is becomes a complete hassle trying to decipher the random words along with have to start over if you input the incorrect verbiage. They do offer a layer of security but are being hacked more and more each day by developers using BOTS and/or having a someone complete CAPTCHA's all-day long getting paid .65 for every 1000. Now imagine if you have bad vision and need to go online for something, it is a complete nightmare and make the online experience not very enjoyable for anyone. At first you had some kind of text-based authentication which was single word and those usually are random letters, numbers and symbols but those can be easier broken, so along came RECAPTCHA which use any two random word to authenticate. These words cannot be read half the time and sometimes the wording combination is offensive.. Imaged-Based Authentication is going to be the next generation of Authentication and will provide users with another layer of protection far beyond CAPTCHA

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