Since the captcha from the field for entering blurry words and numbers turned into a point where you just need to click the mouse, we began to forget about the torment caused by the need to recognize extremely fuzzy characters.

Captcha - how much of this word for a person who had to meet with her every day. At some point, not too long ago, it seemed that only protection that an ordinary person could hardly cope with would help escape from bots. This belief has generated many UX-monsters, which will be discussed in the article.
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Modern captcha tries to be invisible, but it has not disappeared altogether. Systems determine the person in front of them or the bot, studying cookies, IP-address, cursor movement and keystrokes on the pages. Regardless of how the captcha technology is implemented, everything is built around the idea of ​​creating a task, difficult to solve for computers and simple for people, but not always in practice, the questions and answers are obvious.



Captcha is an automated public Turing test that can be passed by a person, but not a computer. Initially, captcha relied on a person’s ability to identify and understand visual / audio signals, which were extremely difficult for bots to make out. Such mechanisms were imperfect: users themselves did not always understand what was required of them. Computers, in turn, learned to recognize objects even on highly noisy images.



ReCAPTCHA: Latin letters and numbers of variable length, distortion, noise, variable background color - at the time of its appearance it caused tons of suffering for users. Today, you will see (or remember) only a few examples that even people could not cope with before (in some cases, bots coped with captcha better than people).

Video captcha

A Canadian startup NuCaptcha showed video captcha: symbols running along a curved line, from which a person was asked to recognize the last three. A research team from Stanford University quickly created an algorithm to break into this video technology. They also circumvented the protection of the usual captcha and the audioCAPTCHA project, aimed at working with visually impaired or blind users.

Game Captcha

Startup Are You A Human with the help of PlayThru technology offers to play a mini-game in which a person needs to select the desired object from a number of those present and place it in a certain place. Although this method seemed to the user more understandable (and logical), it is also periodically subjected to hacking attempts . This captcha is ineffective because it does not have enough elements to prevent the possibility of busting options. In addition, the probability of getting the correct answer is high, simply by accidentally guessing the desired sequence of actions. Every time a captcha tries to do something “pleasant” and exciting for the user, a security hole arises.

Artistic captcha

The website of geee.net trash graphics could not do without a captcha, which would scare visitors by its very appearance. Users are asked to draw what they see in the picture. Artistic captcha can not be considered a full-fledged tool of protection - this is a joke, designed to attract attention, but there is no more humor in it than the truth. Captcha with due diligence you can go.

Matcapcha

Having survived a rapid flourishing, the mathematical captcha quickly went to zero, since it would be no problem to answer the question of how much “3 + 3” will be for bots. The trick here is to find a puzzle that would be difficult for bots, but solvable for humans. Captcha, as in the example above, can be solved by having a textbook on mathematical analysis or access to WolframAlpha on hand, but how many people are willing to spend their personal time looking for an answer?

Metal CAPTCHA

Instead of a series of letters and numbers, Metal CAPTCHA asks users to decipher metal band logos. If you are not familiar with this genre of music, it will be difficult for you, but you can always use the search by images. Unfortunately, the project is now closed (for obvious reasons).

Programming captcha

Codecha is a programmer captcha whose solution requires writing the body of a function that solves the task in one of the selected programming languages. It protects not only from bots (partially), but also from all people who are not familiar with programming (completely).

Unreadable captcha

An example of a Chinese captcha from the site 12306.com, on which you need to mark a picture (or pictures) with the image of agate. The difficulty is that the picture is of low quality and size - in the illustration above you can evaluate it in its original form.

Radio captcha

Captcha from the now deceased radio forum flyback.org.ru was used when registering a new user. In captcha, it is proposed to solve the problem of determining the energy stored in a condenser. Task description: the transformer has a transformation ratio Ohm Ohm and Ohm All circuit elements are ideal, the voltage drop across the diode is zero. Input voltage: sinusoidal 50 Hz, with a valid value of 58 V. Determine how much J of energy will be accumulated in a capacitor ?

The Hindus hired for a penny are unlikely to cope with such a task, solving any symbols on the pictures of standard captcha. It will also scare away all users who do not have sufficient knowledge.

Traveling captcha

They Make Apps created a special slider in which the cursor should be placed at the end of the line in order to register on the site.

Graphic captcha

MotionCAPTCHA is a plugin that prompts the user to repeat (draw) a shape from various pictures.

Interactive Captcha

Interactive captcha . Four different sliders must be set in the correct position for posting a comment on the blog - the color of the slider must be selected according to the specified field.

Geometric Captcha

This geometric captcha is about the same level as the mathematical one — equally challenging tasks for humans and equally ineffective in front of bots. If you answer randomly, you have a 15 percent chance (1 chance out of 6) to give the correct answer, which, of course, does not allow for a good level of security. In order to answer the captcha question, you only have 30 seconds.

Multilingual captcha

Captcha from sveit.com (now abandoned) was based on mixing several languages ​​at once.

Hidden code

But the captcha hidden-3d.com is very much alive. You just need to find the hidden code in the image.

3D image

3D captcha. In fact, nothing complicated if you know programming.

Logical puzzles

A logical riddle, not a captcha. An example is taken from a compilation , and on which site this type of captcha was used is difficult to determine now.

Read points

This is not a captcha for the blind, as one might think, but the world's first captcha made using Braille. Now abandoned and nowhere, fortunately, is not used.

Note CAPTCHA

Musical captcha for the site of musicians. On the server, a picture is generated from (pseudo) randomly selected four pictures of notes and pauses. The names of the pictures - numbers from 0 to 13 - correspond to the position number of the note on the stave, starting from the bottom incremental. The key is also random - bass or treble.

Captcha we lost

Since there are ways to crack every new generation of captchas, machine learning algorithms give computers more and more opportunities to comprehend the world around them. At some point, captcha began to be used for teaching AI, which begins to act on the same principles on which our brain works.

The evolution of captcha is evidence of AI progress. The first reliable puzzles that were used to protect against bots ten years ago can now be solved automatically with the help of computers in 99.8% of cases. While computers are getting better and better at solving puzzles, people can prove their humanity by doing other types of tasks.

In addition, a lot of captcha services have appeared, which serve thousands of living users, ready for a little money to solve any captcha that can be understood.

At one time, Mail.Ru Group came to the same conclusion: this is how the intellectual captcha service appeared, which does not require a person to undergo an inspection. We have more than 100 million users, and most of them are authorized. And this means that with a request for our domains, session cookies are transmitted, by which we identify the user, and then we retrieve his profile, statistics, spam rating, etc. All this information is fed to the input of the classifier algorithm, and at the output we get an assumption about whether the user is a person or a spam bot.