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What is CAPTCHA and why it is used?

Updated on March 6, 2013

Where have you seen CAPTCHA

We all are familiar with CAPTCHA.Even a normal Internet user have come across many CAPTCHAs.Most websites like Yahoo,Microsoft any many others use this program as a part of new users Sign up and in many more sites where we post comments,order products and many more.In all these cases we come across a distorted text between images where we are supposed to type those text.Unless we read those text and type in correctly,we are not allowed to proceed.Sometimes,the text may be too much distorted that you can't read at all.Once you type it wrong,you have to come up again with another distorted text.Feel fed up with those?Why all these useless?Have you ever thought?It is true that we all spent a few seconds to read and type those text correctly.But the fact behind this is that it's a way to ensure that a human is using the interface and not any Computer programs.

What is CAPTCHA?

CAPTCHA is program, that generates tests like asking user to read distorted text and type in a specific area.It stands for Completely Automated Public Turing Test To Tell Computers and Humans Apart .It was developed in Carnegie Mellon University to be used by Yahoo.

CAPTCHA in Google

CAPTCHA in facebook

CAPTCHA for Internet Security

Preventing bogus comments

You might have come across bogus comments in blogs.These are comments which make no sense,just jumbling up of letters and is posted by an unknown user.An example is shown below.

Author : zsruspgzgtw (IP: ,

E-mail :


Whois :


iszwUT zlaqlsxekynz, [url=]ddklkpdrneog[/url], [link=]nxzhyytqnuwe[/link],

Using CAPTCHA for posting comments ensures that a human user is posting comments.Also,the user need not sign up for posting comments.Just entering the CAPTCHA text correctly ensures that a human user is posting the comment.

Preventing bots in Website Registration

There are may websites that allow free sign up.'Bots' are a kind of attack that signs up in many such websites.Using CAPTCHA in such cases can ensure that only human users sign up and create accounts.

Dictionary attacks in password systems

Dictionary attack is a kind of password hacking by entering all the words in dictionary as password.Spammers often use this kind of attack.Asking user to solve CAPTCHA after certain number of password entries prevents this kind of attack.

Protection against worms and spam

Using CAPTCHA does not accept any mails or comments from users other than humans.In this way it provides protection from worms and spam.

Preventing abuse in online polls

Using CAPTCHA in online polls prevents spam voters.Solving CAPTCHA here ensures that only humans cast votes.This also makes such voting contests trustworthy.

Use CAPTCHA in your site

Using CAPTCHA in your site can help you to avoid spam and makes your site secure.You can use the following link to use CAPTCHA in your site:


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    • profile image


      4 years ago

      best example for CAPTCHA in google!!rofl....

    • leeba ann varghes profile imageAUTHOR

      Leeba Ann Varghese 

      4 years ago from India

      @Johnf991...sure sure..iam happy as well.

    • profile image


      4 years ago

      Id forever want to be update on new articles on this internet site, bookmarked ! . eadcdbdfgkgd

    • profile image


      4 years ago

      Do you mind if I quote a few of your posts as long as I provide credit and sources back to your weblog? My blog is in the very same niche as yours and my users would truly benefit from a lot of the information you present here. Please let me know if this alright with you. Thank you! aegkecedcfdg

    • Cogerson profile image


      6 years ago from Virginia

      I think CAPTCHA is becoming more popular I see more and more websites using it...including HubPages when you are sending e-mail...thanks for sharing this information...voted up and useful.


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