Captcha is an acronym that corresponds to the English expression “Completely Automated Public Turing test to tell Computers and Humans Apart”. This phrase refers to a Turing test that is carried out in a public and automated way with the aim of differentiating people from computers (computers).
To understand what a captcha is, therefore, we must know what the Turing test consists of. This test is developed with the objective of distinguishing, in an exchange of messages, a machine from a human being. In the Turing test, an individual controls the test; in captcha, on the other hand, a machine manages the whole process. That is why it is said that the captcha is a Turing test carried out in the opposite direction, since a computer executes it to discover if the participant is another machine or a person.
According to DigoPaul, the captcha consists of a test that generally forces the user to enter a series of characters that appear in a distorted image. This test is based on the inability of machines to recognize deformed characters. Therefore, the one who manages to complete the captcha successfully is a human being.
Since this recognition system has been around for a long time, over the years it has taken on various forms, many of which no longer require text input. In some sites a box with several images is shown and the user is instructed to select some of them, giving him a well-defined criterion; For example, they may be photographs of the public road, of which you only have to click on those with a traffic light.
This system is used on websites to avoid unwanted messages or certain actions performed automatically by a machine. On many sites it is necessary to overcome a captcha to post a comment: this prevents massive advertisements distributed by computer programs.
Beyond its effectiveness, the captcha has several shortcomings. A human with a visual impairment, for example, might have trouble recognizing characters and passing the test.
Although in general terms we associate the concept of captcha with the fight against piracy and computer attacks, this system is also used by those who practice illegal activities, although they do not do so directly. For example, people who are dedicated to distributing movies, books, music and video games for free often seek a monetary income through companies that provide them with a system that forces the user to look at certain advertisements before accessing the content and, finally, to overcome a captcha.
On the other hand is the recaptcha, sometimes written reCAPTCHA, an extension of the captcha that is also used for text recognition in images. The main difference between the two applications of the test is that in this case the text sources are books or documents of great value that have not yet been digitized and archived in libraries, and the user’s work is used for the same purpose. In short, recaptcha reduces the percentage of virtual fraud while enriching cultural heritage.
The concept of recaptcha arose based on the fact that a text in an image that for a computer can be very difficult to understand, for a human being can be very easy to read. In other words, thanks to this movement the text digitization process is considerably accelerated, while the recognition technology continues to slowly advance until it reaches the level to be able to completely do without human labor.