By the way, why are captchas called captchas?

You type regularly on the net to sign up for a site or submit a form. These are the captchas. But do you know what the name means?

Are you about to register on a site, change your password or make a purchase, but have you received an instruction asking you to rewrite the letters that appear on an image or indicate images that show a particular item? This is called Captcha and this type of request is very common on the web.

This procedure is at first glance decked out with a very strange name, but it is actually an English acronym. If you open it fully, it means ” Fully automated public Turing test to distinguish computers from humans “, this is ” Fully automated public Turing test to distinguish computers from humans ” in French.

This is the central goal of the captcha: to verify that the origin of a request (accessing a form, changing the password, etc.) is someone and not something. The goal is to eliminate machines designed to harm the system, such as dumping spam into mailboxes – that’s why it’s critical to prevent these bots from creating accounts.

A Captcha on a computer // Source: Adam Donkus

The Captcha’s name refers to Alan Turing, this British mathematician and computer scientist who made a notable contribution to conducting World War II, helping to break the Enigma mechanism by which Nazi Germany sent coded instructions to its strengths. The resolution of Enigma is said to have shortened the war by two years.

His name was also used for the Turing Prize, awarded since 1966 by the ACM (Association for Computing Machinery). It is considered the equivalent of the Nobel Prize, but in computer science. In any case, it is an extremely prestigious and necessarily highly coveted recognition. But it is mainly because of the “Turing test” that his name has passed to posterity.

This test designates an experiment consisting in seeing if the answers given by an artificial intelligence are sufficiently elaborate that it can no longer be distinguished from those that a human being would give – obviously without knowing in advance whether it is a human being or a machine that he replies. In short, the Captcha is a variation of this Turing test.

bot captcha
The Captcha is used to verify that you are not a robot // Source: Gwydion M Williams

Why do sites use Captcha?

The main motivation is security to limit the annoyances on the web. Computer programs roam the net to spam or try to deceive Internet users, to collect personal data, to trick you into buying dubious products, and so on.

Hence the interest in guaranteeing the use of contact forms, access to comments and exchange spaces. Signing up for a discussion forum, for example, is often subject to resolving a Captcha, validating the account via a link sent to the email, and sometimes admin approval. Challenging, but sometimes necessary.

Similar barriers exist on contact forms, in comment areas on blogs or sites, but also to access this or that platform, such as email providers such as Outlook, Yahoo and Gmail. These webmails are also recurring targets, because email is a first-rate tool for trying to deceive someone.

How does Captcha work?

There are several types of Captcha, which verify and confirm that you are not really a robot. These are very easy tests for humans (at least they should be), but intractable for robots. But with advances in computing, the opposite tends to happen: paradoxically they have become more difficult for humans to solve.

The most common captchas are text-based. They form a series of distorted texts and figures that must be rewritten before validating their registration on a site. Sometimes, “parasitic noise” is added to the background of the image, with the aim of distorting optical character recognition. This is the case, for example, in the image below.

Text captchas form a group of numbers and letters // Source: Shinseungback Kimyonghun

There are also image captchas, in which you have to select a series of visual elements based on a particular request: designate photos in which you see a car, a pedestrian crossing or an animal. We can also mention the Calculation Captchas, in which you have to find the answer to a simple mathematical equation and write it down in the box provided for this purpose.

Of course, it can happen that you get it wrong on an equation or not be able to identify the images that the Captcha asks you. In this case, you can request another test using an icon which is usually found to the right or at the bottom of your Captcha. Or to request an audio reading of the Captcha (if it is textual).

The fact is, Captcha’s future could be numbered. Faced with the increasingly important capabilities of systems to bypass these devices, companies such as Google and Apple have developed strategies (the former with reCaptcha, the latter with Privacy Access Token) that make it possible to distinguish between humans and robots based on other signals.

Leave a Comment