How Do CAPTCHAs Separate Humans From Machines?

Have you ever wondered why every time you'd like to comment on an article, blog posts or download a file on different file sharing sites like 4shared and filesonic, CAPTCHAs always require you to enter some twisted and hard to decipher words? What's the purpose of those contorted words anyways? Well, for our own benefit and information, CAPTCHAs were invented by computer scientists to prevent spamming machines from posting such unwanted ads or links in sites. CAPTCHAs determine whether a visitor who tries to post is a human being or a computer. People who invented CAPTCHAs learned and observed that the easiest and effective way to block spamming machines is by using images of language. Spammers can be detected easily and be deceived by using such images of language that are texts in a randomly generated and uniquely constructed manner such that a human can hardly read it. But for a computer to decipher, it would be impossible.

                          Image via Wikipedia

Though the internet are made up of many words, believe it or not, computers cannot read them. Its very hard for a computer to understand languages because they cannot adapt to the hard and fast rules that computer programs demands. Therefore, coding languages have to be made as a substitute because human languages are very eccentric and unreliable. And with this difficulty, CAPTCHAs uses the human's unique ability to read letters that are reshaped, twisted and stretched being in such a way that a person can still decipher it.

Do you know where did CAPTCHAs got its name? The acronym actually stands for "Completely Automated Public Turing test to tell Computers and Humans Apart". Though the words themselves tell its meaning, the words "Turing test" actually came from a computer theorist who invented it, named Alan Turing. The test was used by computer scientists to see whether a machine or computer can speak or converse like a human being. Thus, the principle is still the same, it is only used oppositely. Computer scientists have used CAPTCHAs first at Carnegie Mellon University in the year 2000. 

Have you ever questioned yourself why CAPTCHAs never used images of things but only letters? Images like  a beach or a dog? This is because images does not have a concrete or exact answer. Images can generate a wide variety of answers. A beach for example, can have the following responses like ocean, sand, people, sunny and many more. While for letters and words, unique answer can be given. Also, letters are much more easier for humans to decipher and for the programmer to precisely use it in his program.=)

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