Why am I asked to Verify A Text I See below in many websites?

Ooooof! You may wonder isn't there any specific name to mention those verification texts rather giving such a long Title to this post.! The answer is of course YES. It is abbreviated as CAPTCHA.

What is a CAPTCHA?

It is the abbreviation of 'Completely Automated Public Turing Test to Tell Computers and Humans Apart'. This is a kinda 'Human Interaction Proof' (HIP). Hope you easily remember what am I talking about. See the pictures down :

Courtesy: www.solona.net

Coutesy: www.technorrhexis.com

What? Is this a test to distinguish Humans and Computers? Why do we need this test?

This is often called as Turing Test, named after the man - the father of modern computing, Sir Alan Turing. He was the one who researched about the level of computer capabilities. 

CAPTCHA is nothing but a warped image which contains a words(or words) which is bent and folded. The result of the test is if it could be read and typed correctly, it must be a human. Else, a computer(malware).

CAPTCHA is used mainly to avoid mal wares accessing a website. Some of the situations explaining the need of the CAPTCHA are as below:

Who uses CAPTCHA?

1. Registration Forms of Websites which provides free e-mail servicesFor Example, Websites like gmail and yahoo mail use CAPTCHAs to prevent spammers from using malwares to generate hundreds of spam mail accounts.
2. Ticket BrokersCAPTCHA applications help ticket scalpers who book bulk tickets without limit at once it is available in the web and stock it. When demand increases, they sell it in a price higher than its original value.
3. Websites containing Interactive Comment Boxes(like blogger)
   CAPTCHA prevents bots posting rude comments about administrator automatically.

 How CAPTCHA works?

One of the above victims are called as Administrators of CAPTCHA. The software used to create a CAPTCHA is known as 'reCAPTCHA'. First, the administrator of the CAPTCHA scans a book digitally using reCAPTCHA. It compares the text entered by the user(seeing the image) and verifies it with the original one. If it matches, the site confirms that the user is not a computer. In order to increase complication, the warped text image is blended with randomly generated background images. For users who are visually impaired, and alternative AUDIO CAPTCHA is used.