A Little Bit of Information About Image Captcha

This article explains how captcha works, why it's necessary and where it comes from - and provides a lot of interesting facts along the way.

A Little Bit of Information About Image Captcha :

If you have ever attempted and failed to log into an e-mail account or any other online account, then you will probably have encountered image captcha at some point. That's the technical term for the little box of unusual looking text that crops up and asks you to type what you see. Sometimes it will come up when you've entered an incorrect password a few times, other times it will appear as soon as you try and enter any data into a form. But what precisely is captcha, why does it exist? And what does it have to do with hacking?

Captcha Versus Robots

First of all, what does captcha even mean? Well technically it should be 'CAPTCHA' because the word is actually an acronym (meaning each letter stands for something) for 'Completely Automated Public Turing Test'.

So now the question is: what's a Turing test? Well psychologists and computer scientists will know that a Turing test is a test designed to test the intelligence of a machine and/or to distinguish machines from humans. In the classic approach, this is accomplished by sitting one person on MSN and then getting them to identify whether they're speaking to a computer or a real person. If they can't distinguish between the computer and the real people, then the computer has passed the test and the AI can be considered really rather good. Now we could talk about the Turing test for ages (it's a fascinating topic), but all you need to know is that captcha is essentially a different kind of test that only needs to catch out very basic computer 'scripts' that perform a specific task: in this case, guessing passwords.

Enter: Brute Force

Specifically, what captcha is attempting to prevent, is the use of the 'brute force' method of hacking. Brute force essentially means running a program that enters countless combinations of password and user names into the correct fields until it hits a match and gets through. This works using a 'pass list' which is essentially a huge list of common words, or in some cases will generate those words randomly using algorithms. Usually for popular sites someone will have an obvious combination of Johnsmith2013 and 'Password1234' as their username and password combination. As such, the owners of these sites needed to introduce something that would block this kind of hacking, and that's where 'captcha' comes in - after three attempts the script will then need to be able to analyse that complicated image and try a username/password combination, and will most likely get stumped by the process.

Anti-Spam

Meanwhile, when you encounter captcha on a forum or a web form, that's there to try and prevent automated programs from promoting products on other websites. This is a technique that some lazy online 'businessmen' will use to try and spread their message far and wide without putting the time in to market it properly - and without captcha or some other kind of spam filter a website owner can end up with a forum covered in spam that no one wants to use.

The downside of this is that it can be a nuisance for real users to have to use regularly though - especially on a mobile for instance - so webmasters and service providers need to choose between heightened security versus heightened convenience.

Other Uses for Captcha

Captcha has come a long way since it was first used, and these days is often used for a range of other clever purposes. 'Recaptcha' describes captcha put to good use - where the answers that users enter are actually useful and end up going towards a greater cause.

For instance, Google uses recaptcha in order to digitize written books. Here the books are scanned into the computer and then analysed using OCR (optical character recognition), but while this is effective it will still leave thousands of words and phrases that the scripts are unable to identify. Those words are then presented to users as part of their recaptcha test (a long with some letters/words that are known) and the results of correct answers will then be added to the digitization process.

Captcha and recaptcha then are very useful and powerful tools when used the right way, and are an integral part of the arms race between hackers and security experts.

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Author Bio :

Nancy Baker, the author of this article, is a freelance blogger who is currently writing for, Cellphone Unlocker, suppliers of wholesale unlock codes. She enjoys reviewing the latest gadgets and applications that hit the market. You can also follow her on Twitter @Nancy Baker.

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