Wherever we go on the internet, we encounter CAPTCHAs, those twisted words that block or enable entries on websites. Need to post an ad on Craigslist? There’s a CAPTCHA. Want to comment on an article or blog post? There’s a CAPTCHA. So why do we have them? They were invented to block spamming machines from posting wherever they want. In order to keep out spammers, a CAPTCHA has to effectively test if you are human or machine. Computer scientists figured out that one of the easiest ways to do that is to use images of language. In order to deceive spammers, the images of language take randomly generated text and manipulate the image, so that a human can barely read it, but a computer trying to take a picture of it cannot. (You’ve wondered about CAPTCHAs, but you probably have also been curious what the i in “iPhone” stands for. The complex and interesting answer lies here.)

Even though we read words on the internet, the internet and computers are not made of words. In fact, computers often have a hard time understanding languages because they do not conform to the hard and fast rules that computer programs demand. That’s why coding languages have to be invented: human languages are too irregular. This is also one of the reasons it is so hard to create an intelligent robot. So, CAPTCHAs take advantage of the uniquely human ability to see letters that have been stretched or manipulated and still be able to decipher which letters they are.

The term CAPTCHA was first used by computer scientists at Carnegie Mellon University in 2000. CAPTCHA is actually an acronym that stands for Completely Automated Public Turing test to tell Computers and Humans Apart. That’s a pretty straight-forward title, except for the Turing test part. What exactly is a Turing test? Alan Turing was a computer theorist who invented the Turing test which humans use to see if a machine can converse like a human being. A CAPTCHA is actually an inverted Turing test whereby a machine tests to see if you are human or not, but the core principle remains.

You may wonder why CAPTCHAs don’t use images of things other than letters, like a beach or a dog, but images are harder to have an exact answer for. A picture of a beach could generate a wide variety of responses–sea, sand, sunny, ocean, and so on–but a CAPTCHA that uses letters is paired to a particular answer. Letters, unlike images, are able to be deciphered by the human eye and programmed precisely by whoever creates the CAPTCHA.
Do you think computers will ever be able to decipher CAPTCHAs?


  1. Clementine007 -  October 17, 2013 - 3:49 am

    I have decided that for me the real purpose of CAPTCHAs is for me to test how much I really want to be on the web site. Three failed CAPTCHAs and I’m out. I am mostly out!

  2. The Ceej -  October 9, 2013 - 6:56 pm

    I’m not going to read your article because I reject the premise the headline sets up.

    The question is not, “How do CAPTCHAs test our human identity…” They don’t. That was never their purpose. Anyone who says it is or was is either a liar or an idiot. Bots can solve CAPTCHAs easily. No bot in the history of the internet has ever been thwarted by a CAPTCHA…

    Humans, on the other hand, almost universally have consistent problems. It’s a bane on the human internet experience while bots don’t mind them. They breeze right through them.

    The real question is, “What is the REAL purpose of CAPTCHA and why the conspiracy of silence?”

  3. Jeevanand -  October 6, 2013 - 3:09 pm

    captchas are highly idiotic..automated robo software can decode 70% of captchas…there are at least 20% even humans cannot decode..the creators of captchas are highly idiots…if the computer cannot do a simple calculation,1+2 = , on its own, then why there is need of developing highly idiotic captchas..no fundamental approach by idiots who create captchas

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    Wow, awesome blog layout! How lengthy have you ever been blogging for?
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  5. Tom -  January 20, 2013 - 2:36 pm

    So, the capcha words are all all actual words? This makes it easier for me now.

  6. MOJAPELE7 -  September 26, 2012 - 6:01 am


  7. al3ab -  July 14, 2012 - 3:49 am

    that’s true, I would prefer a method like a mini flash game or to ask a random question for which a robot can’t recognize answer, keep on good work

  8. fred -  July 1, 2012 - 8:16 am

    Captcha’s are great for removing traffic to a website – it helps in turning away casual users so that those that run the site don’t have to deal with the hassle of having to run a successful site.

  9. Dev Baisoya India -  June 25, 2012 - 9:27 am

    but for those who are unable to read.. there should be option to calculate something… like addition subtraction or multiplication of two numbers… i have seen it on many websites..

  10. Dev Baisoya India -  June 25, 2012 - 9:22 am

    I don’t think captchas are hard to read.. they are very easy for a human being.. but not for a robot or a software.. it never takes more than 10 seconds to read complete captcha of 6 letters.. and its all about your security.. isn’t it even if it takes more than a minute?

  11. Professor Know-it-all -  June 12, 2012 - 3:33 am

    I accidentally added another a in freak so it is not freaak so don’t look it up on dictionary.com

  12. Professor Know-it-all -  June 12, 2012 - 3:31 am

    If you can’t read the CAPTCHA then don’t freaak out there is a sound button near the CAPTCHA so the computer can read it out to you. This can solve 95% of your problems with CAPTCHA.

  13. Bryan -  June 12, 2012 - 3:27 am

    In the game , maplestory , there are CAPTCHA you would have to enter before logging in to your character , but even with that , Spam bots have found ways to crack into the game … CAPTCHA is like a waste of time as humans need to type in and Spam bots just like hack their way in …

  14. Elliot -  June 11, 2012 - 10:12 am

    CAPTCHA’s are hard some times, and defiantly can be annoying after so much time. On the Other hand, Using a CaPTCHA is less annoying than getting hundreds of robot emails. posts, etc.and also less annoying than getting hacked. One day I believe computers will Be able to figure them out or crack/hack them. SO right now you should be happy they are just the way they are (even though they can be hard). Learn how to read them.

  15. Elliot -  June 11, 2012 - 10:10 am

    CAPTCHA’s are hard some times, and defiantly can be annoying after so much time. On the Other hand, Using a CaPTCHA is less annoying than getting hundreds of robot emails. posts, etc.and also less annoying than getting hacked. One day I believe computers will Be able to figure them out or crack/hack them. SO right now you should be happy they are just the way they are (even though they can be hard).

  16. Franz -  June 11, 2012 - 12:33 am

    how a very good explanation demosthenes. that is right if CAPTCHA is make to easy its useless to make a CAPTCHA word. and have always a gap between robot and humanity. thanks guys

  17. Ness -  June 10, 2012 - 8:25 pm

    I saw a unique captcha where you have to drag something to a respective image eg. “Drag the juice to the bottle”. Then there are four different images, you have to choose the juice and be able to drag it to the image of the bottle standing to the side. One example is when you sign up for a 6Theory account. Look it up!

  18. Wheatley -  June 8, 2012 - 4:43 pm


    2.)I wonder if GLaDOS can read CAPTCHA’s

    3.)@Demosthenes, Did you read Ender’s Game?

  19. Demosthenes -  May 20, 2012 - 12:16 pm

    CAPTCHAs are good. It doesn’t matter if some people can’t get in, as long as they keep a bigger percentage of computers out. But I would like these people to READ THE ARTICLE. Maybe if you had, you would be talking about the right thing. As of now, there are 280 comments, and about 3 of them are answering the right prompt. And more than 200 of them say “Malik, you’re right.” IT’S BEEN SAID BEFORE! Ironic, isn’t it, that the forum about CAPTCHAs has no CAPTCHA. Anyway, computers will eventually learn to decipher the CAPTCHAs, as they’re not that hard. They’re designed so that any human can understand them. And as robots and computers are getting closer and closer to human intelligence every day, they’ll soon learn how to bypass them. Then they’ll become harder, and then maybe we’ll have a reason to complain. But not now. And even then, maybe they’ll switch the format to something different that will be just as easy. But this is one of humanity’s only advantage over machines. Don’t let them infiltrate forums like this one. Learn how to read CAPTCHAs.

  20. Question! -  May 2, 2012 - 4:59 am

    Those who say there are’nt easy, are you sure that you are human biengs? lol.

  21. astha gupta -  February 28, 2012 - 6:06 am

    why don’t we use special characters in captcha..??although it may be difficult for computers to judge..?

  22. imformation -  November 23, 2011 - 9:19 am

    i see it as this is a site where if you cant get on like facebook or something you and others can talk on this website and tell people im on it cause its educational

  23. Chovie -  November 21, 2011 - 7:45 am

    CAPTCHA sucks sometimes… like when they put foreign languages in it or math equations haha

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