What is CAPTCHA and why it is used
Posted On: September 22, 2009
CAPTCHA stands for “Completely Automated Public Turing test to tell Computers and Humans Apart”. This is a challenge-response test used on web-forms to ensure that the form is filed in by a human being, or in other words it is a form of protection from bots (computers) filling out forms.
Why would a computer fill out forms?
There are two main types of forms that need protection, one is a registration form and another is a contact form. Sites requiring registration usually have some kind of messaging systems and using a computer program people can create multiple accounts and send out spam to other users. Contact forms on the sites usually deliver messages to the site owner; if it is not properly coded, may be used to send spam to other email addresses. In both cases CAPTCHA stops computers from submitting a form.
Different types of CATPCHA
Most often used is the image recognition type, here are few common samples:
Another type is questions like “Sum of one and two” that is written with words or with digits “1+2=” (The first sample has to have few languages options or it will create a problem for non English speaking users).
Some people overuse this protection method and end up with forms that are impossible even for humans to submit. So while trying to protect, one has to keep in mind that sites are done for people to use. The next post will provide a sample CAPTCHA using PHP.
Michael Pankratov
Associated tags:
PHP,
Security,
Form,
CAPTCHA
Comments:
Michael Pankratovs wrote on
October 5, 2009 at 10:42
To see how to implement CAPTCHA using PHP click here
Florences wrote on
May 31, 2011 at 08:48
Wow, your post makes mine look felebe. More power to you!
nilesh patils wrote on
October 3, 2012 at 09:54
Sir i got ur point. But what exactly that mean? What exactly CAPTCHA do in the process of depressing the spamming and enhancing security? Because human being is able to identify what is hidden in CAPTCHA. so any spammer can still do what he wants, no? Please reply
Michael Pankratovs wrote on
October 8, 2012 at 17:33
Yes, spammers can read it, and can submit forms manually, and nothing will stop them from doing it. The reason why CAPTCHA is used, to block computers from doing it, since manually it takes man power to do and not that fast, when if a computer does it, you will get 100 submissions a minute for you form. Thanks for the question!
shantus wrote on
November 8, 2012 at 21:25
but sir, even after the captchas have been introduced we can see a lot of bots chattin in yahoo messenger chat rooms...why so????
Michael Pankratovs wrote on
November 14, 2012 at 11:42
Hello Shantu,
Even with captcha robots can submit forms, but their success rate is less than 10%, so it takes very long time to submit once.
Also in some cases there are real people creating profiles and accounts in messengers, but then robots send spam through it.
