CAPTCHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart. CAPTCHA is a difficult acronym but is a very useful tool in differentiating robots from humans. In short, it is a simple test to detemine if the user is a robot or human.
Now-a-days, websites became the identity for many businesses. Many companies have their sites for online business. These companies offer a lot of free services to their users. The only thing is to register on the site. So, many people exploit the offered free services by duplicate registration. They write a computer program that can automatically register on the site and then can use the offered services. CAPTCHA is developed for avoiding such spam registrations on the site and exploitation of the offered free services.
How CAPTCHA works?
CAPTCHA is a distorted image containing short text. It is displayed in such a format so that only human eyes can recognise the alphabets clearly. At the time of registration, such image is displayed on the form and the user is asked to write the same text in given text field. The robots fail to recognise the short text. Thus, website owners can prevent robots from registration and can ensure that all the members using free services are humans.
Thus CAPTCHAs prevent automated posting to blogs and forums. CAPTCHAs can be used further in avoiding spam emails. Apart from these usage of CAPTCHAs; it is criticised that people with poor eyesight or blind people will be unable to use the web services offered.