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 |
Web development