What is captcha? Why is captcha required? What to do when asked to enter a captcha The captcha field is required.

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Captcha is an anti-robot protection tool that prevents bots from performing any actions.

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Often it is a picture with numbers that must be entered in a special field. A robot will not be able to understand what numbers are drawn, but a person will be able to.

Let's say you come to your relatives with a work laptop to show them photos. To prevent children from getting into your computer and deleting anything while your whole family is sitting at the table, you set a password.

Captcha performs similar functions - it limits the capabilities of bots.

A captcha for a website also performs this function, limiting access to automatic programs to the capabilities of the resource.

What types of captchas are there?

Machine intelligence is constantly evolving. Developers create bots, attach them to neural networks for training. It's a race of increasing artificial intelligence and ways to protect against it.

New verification methods are being developed. Eat different types captcha.

SI Captcha Anti-spam

This option can be found on most resources on the Internet. The code is a mixture of letters and numbers in the picture. There is also a listening function, which is necessary if the text is not clear.

reCAPTCHA

Used for social networks or platforms that require authorization. The modern version is a block of images and a word to which the user-selected pictures must correspond. One of the giant projects that uses exactly this method is VKontakte.

Math Comment Spam Protection

Popular captcha for blogs and postal services. To confirm that you are not a bot, you will need to perform some simple arithmetic and enter the result.

Which one to choose

To understand which captcha is best for your project, let’s briefly look at the popular options.

Text

IN Lately Programs are becoming popular that allow you to automatically display the correct version of a word, despite any attempts to encrypt it. If your resource is quite popular, spammers will definitely use such a utility.

Consisting of a question

This captcha looks something like this: “Write the number eight hundred ninety-seven minus four.” The main disadvantage is that manufacturers of protective equipment mainly live abroad, and not everyone can understand the meaning of a question in a foreign language.

Picture

For example, “Select all images that contain deer.” Interesting presentation, but sometimes the pictures are so Bad quality that the horn sticking out from behind the bushes is simply not visible.

Earning money by entering captcha

There are special services that spammers use. Captcha is entered by people small fee. This is a dubious method of making money. We repeat: deception is bad.

We talked about what captcha is. The owner of each site is interested in ensuring that only “live” users who are interested in this portal register on his resource. And bots are only good in Telegram.

Hello, dear readers of the blog site! Another concept that almost all Internet users encounter sooner or later and which I would like to introduce you to is captcha. I think that many, when registering or logging in to websites (and not only) already had to fill out an additional column.

To successfully complete the process, you usually need to enter numbers, letters or even whole words, depicted in the picture immediately offered, in most cases in a distorted form (using blur, applying various kinds of effects, etc.).

Such unique puzzles can be anything. For example, it is likely that you will be asked to enter the result of a simple arithmetic operation or to arrange images in a certain order by dragging and dropping.

What is captcha and types of this protection against automated spam

All these ingenious tasks and tests that require the performance of actions inherent to a person are created, of course, for a reason, but pursue a specific goal. Which one? This will be discussed below in this publication.

So, let's try to make things clear right away. The Russian-language word “captcha” comes from the complex English abbreviation CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart), which in full translation into Russian means “a fully automated public Turing test to recognize computers and people.”

Why was this test designed? The fact is that among them there are not entirely (or even not at all) legal ones, an important part of which is the sending of spam (), which is a real disaster for users of the World Wide Web.

In order to get rich, spammers use all available means to the fullest. For this purpose, they register en masse on all kinds of resources, including forums and social media. For example, in RuNet the VKontakte site is especially popular in this regard (and details about this social network).

However, you can’t find much out of this manually, as you understand. Therefore, representatives of this contingent make full use of software and configure with it automatic mailing spam And this is a completely different calico. After all, the program (robot) can work without sleep or rest, and therefore has an undeniable advantage.

This is how an avalanche of spam messages hits users. This method is especially annoying for those who use the Internet professionally, for example, webmasters.

Owners of websites (existing on the Internet) know firsthand how spammers’ products can irritate and unsettle. By the way, at the end of the article I will advise you, in my opinion, the most optimal this moment anti-spam tool that you can use on your website.

Therefore, it is quite logical that a protective tool appeared in the form of a Turing test called captcha (sooner or later this had to happen), the noble goal of which is to burn out unpunished spam activity in the bud with a hot iron.

Of course, there are positive changes as a result of using CAPTCHA, however, the result is not as rosy as one might expect. Life does not stand still, and therefore there are constantly messages about the development of new software that can bypass any captcha. Demand creates supply, because spammers are not going to give up and abandon their “gold mine”.

In contrast, the mechanisms of various forms of CAPTCHA are also being improved, which we will discuss below. This reminds me of the confrontation between weapons of attack and defense, which has been going on for several centuries.

For example, in response to the use of spears, axes and arrows, armor was invented, armor was invented against projectiles, and then an armor-piercing projectile, and so on. Our world generally develops largely due to the struggle of opposites.

What types of captcha are there?

Well, okay, let’s leave philosophical maxims for now and get down to business. So, we have established what a CAPTCHA is, which serves as a very effective tool against automated spam. But how effective is it? Much depends on the professionalism and qualifications of web developers, as well as the software algorithms they use.

After all, the very essence of captcha is to make it as difficult as possible for the machine to perform a test that an ordinary person should be able to easily pass. Unfortunately, such an ideal ratio is difficult to achieve over a long period of time due to the existing eternal confrontation mentioned above.

Very often, users spit, forced to go through a captcha that is sometimes difficult to solve. Guess what an ordinary user will do when they see something like this:

That's right, he will leave such a resource, since there is always an alternative on the Internet. Thus, when using these types of CAPTCHA, the website owners themselves suffer, as conversion rates decrease, traffic drops, and potential subscribers and clients are lost.

So, knowing what it is used for this protection from spam, we can formulate the basic conditions that should form the basis for creating an ideal captcha (the ideal, as we know, is unattainable in real life, but we must strive for it):

developing a test that any person could cope with in a minimum period of time, and would be absolutely inaccessible to a bot;
minimizing any data entry;
taking into account the interests of users with physical disabilities (for example, implementing audio support for the visually impaired).

You can easily assess for yourself which captchas you have encountered on the Internet best satisfy the above characteristics. Well, now it’s time to get acquainted with the main and most popular types of tests today, implemented in one or another captcha:

1. Enter text in the form of letters, numbers, words or phrases:

The problem with this type is that the text characters will make it difficult to enter them not only for bots, but also for mere mortals like you and me.

2. Actions with images. For example, choosing suitable pictures (pictures) from several proposed ones that would meet certain criteria. Let's say, to solve the captcha given as an example below, you should select all the images where grass is present:

This type of input is more complex for programs because it involves image analysis. And this represents a serious obstacle for them, although recently to eliminate this deficiency Anti-captcha developers have taken a step forward.

This also includes the compilation of a complete image from disparate parts, which is an inherent human ability for logical and analytical thinking. By moving the details to the right places with the mouse, we get the desired picture (in this case, a human face):

Again, solving such a problem is not an insurmountable obstacle for a living user, but it still takes away precious time, which has always been worth its weight in gold.

3. Using arithmetic or mathematical operations to enter CAPTCHA:

here again it is important not to overdo it and not force the user to “wrinkle his brain” to no avail, as in the example shown in the fifth screenshot above.

4. ReCAPTCHA. This type of Turing test is more attractive to a wide range of users, since it takes into account the interests of people with disabilities (see the list of conditions for achieving the “ideal captcha” located a few paragraphs above), offering, along with a visual option, audio reproduction of the text located in the picture:

ReCAPTCHA is quite reliable and has a high degree of protection against spammers, so it has long been used on many large web resources, including the Google registration page. True, the example above is not entirely successful, since in this form the text depicted is too distorted and is difficult for an ordinary person to reproduce.

Then you have to either select another picture using the update button (circular arrow), or use voice (audio) playback (loudspeaker icon).

In this form, of course, the captcha is more attractive and does not cause obvious rejection.

Along with the leader of the world search, it is worth mentioning Yandex, which is its main competitor in the Russian Internet () and also uses original protection against spammers (YaCAPTCHA), where a code word or a simple set of letters can be offered in Cyrillic:

Naturally, the types of captchas I have given here are only a small part of their entire diversity. Moreover, I classified them according to those characteristics that show variability. You can do the same yourself by identifying other fundamental characteristics by which classification can be made.

For those who prefer video materials text information, you can watch a very popular video about various types of captcha:

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Entering a captcha and assessing the possibilities of bypassing it

So, we have established what captcha means. This is nothing more than a fairly effective means of protection against automated spam. And if you see a sentence like “enter the captcha” in front of you, then you must solve a simple puzzle, the solution of which confirms that you are a living person, thereby ensuring access to the system.

The secret is that RuNet users often visit foreign sites, where CAPTCHA can also be found in one form or another. Therefore, it would be useful to provide a translation of some expressions that may appear in messages accompanying the completion of the code.

For example, on some resources, if you enter characters incorrectly and the resulting error, it is likely that you will see something like this:

“Captcha test failed” translated from English into Russian means “captcha test failed.” The following expressions may also be present (their translation into Russian is on the right side):

“CAPTCHA error please try again” - error entering captcha, please try again;
“please complete the CAPTCHA correctly” - please fill out the captcha correctly.

In this case, you just need to try again.

Next, the question arises: how to bypass the captcha or even remove it, and what needs to be done for this? I will say right away that it will not be possible to do this completely. I already mentioned in today’s article that there is a continuous struggle between the creators of software capable of recognizing complex characters, and, in fact, the authors of various kinds of software tests.

At this stage, no one has achieved a decisive advantage, however, in the future, I think, the existing parity will remain with some changes in one direction or another. This is explained by the interest of both parties (both the owners of Internet resources, seeking to protect themselves from bombardment of spam messages, and spammers, who do not want to miss out on a profitable means of enrichment).

Therefore, spam, of course, passes, especially when using the most modern paid software. But the effectiveness of even the best automatic programs is far from one hundred percent, this is evidenced by the fact that they are thriving online services(anti-captcha), where captcha is recognized by real people, naturally, for a reward.

In this case, efficiency tends to maximum for obvious reasons. However, if you have a need for mass captcha recognition, you should be prepared for the fact that you will part with part of your hard-earned money. You have to pay for everything in this life.

On the other hand, you can make money on such services if you register as an employee. The most popular and, perhaps, . The money you will receive there will not be very big, it’s more likely additional source income.

It must be borne in mind that this work does not require any special skills or knowledge; anyone who has a simple Internet connection can do it. And unskilled labor is not highly valued by default. But if you don’t like it, you can always quit this idea.

The optimal solution for websites is installing reCAPTCHA

Well, at the end of the publication, I cannot help but touch upon the issue of using the most effective captcha on my website or blog. After all, all webmasters know firsthand the “charm” of communicating with spammers.

Perhaps, it was at this stage that a rather productive remedy appeared in the form of latest version of reCAPTCHA(mentioned just above), which is already used by major world services, including, of course, Google. The difference from the old version is that the user just needs to check the box next to the inscription “I am not a robot”:

I have also installed reCAPTCHA on some of my online projects. This antispam tool is not yet available on the site for the simple reason that I am generally satisfied with the work, which is suitable for my comment structure.

But you can easily install reCAPTCHA, for example, on your WordPress blog in order to filter the same comments with the noble goal of making life easier for your visitors. In conclusion, another super video

If you have come across a mini-test on the Internet that asks you to recognize characters in a picture, then you probably know how tedious the task of entering a captcha can be. It’s one thing if you rarely encounter captchas, but if you need to constantly decipher captchas, then entering characters every time will quickly get boring. However, fortunately, there are ways that allow you to enter a captcha quickly or even bypass this type of verification altogether.

What is a captcha and what should you consider when writing it?

Captcha is, as a rule, encrypted characters in a picture that need to be decrypted. The captcha image may contain a wide variety of symbols: letters of the Cyrillic or Latin alphabet, numbers, equations, or even photographs. When entering a captcha, you should be as careful as possible, since an error in decoding even one character will not allow you to pass the test.

Earn money 💰 online by entering captcha All you need is to correctly enter the text from the picture (from the captcha).

You get money 💵 for every captcha you enter.

When entering a captcha, it is not only the symbol that matters, but also its size - take into account the difference between a capital letter and a capital letter, it is also sometimes important to take into account the shape of the symbol, because it happens that the letter “O” is similar to the number “zero”, and the system will not count this when entering substitution.

When solving mathematical equations as a captcha, you should enter only the answer in the captcha field, for example, if you are asked to add two numbers, then the answer to the captcha will be the result of mathematical operations. Another unusual type of captcha is a set of photographs, from which you should choose similar ones. So, you may be asked to choose a photo with drinks from a wide variety of sets of images, in this case you should be careful and boldly choose photos that even have something similar to a drink.

What is the reason for captcha?

Captcha occurs when the system wants to determine whether you are a real person. This is usually required when registering on sites where you are sometimes forced to enter a captcha several times. If you entered the captcha incorrectly, the system will not allow you to complete registration on the site.

The task is especially difficult when registering with mobile devices, for which the resources do not always have the proper version with a working captcha. In this case, sometimes it is impossible to enter the captcha at all and you have to register from your computer.

Captcha also appears on websites when a user displays suspicious activity. If you decide to start spreading spam, entering captcha will become a very common task for you. Of course, you can simply advise not to engage in spam mailings and other suspicious activity on sites, but it happens that this is precisely your current task and you need to distribute advertising on a social network or an announcement on a forum. In this case, it is important to find a way to quickly enter each captcha or somehow skip the check.

Watch the video - How to quickly write a complex Japanese captcha:

Anti-captcha service for manual recognition Real people work on captcha recognition, so the service can handle everything that a person can recognize:

text captchas, graphic captchas: ReCaptcha V2, KeyCaptcha, FunCaptcha, etc.

How to bypass or skip captcha?

Some sites and programs allow you to skip entering the captcha. It is enough to simply leave the input field empty, but this method rarely works. There is also advice from hackers who are used to hacking websites and captchas - in some cases it is enough to simply disable image loading in the browser, so the captcha image will not load and the input field can be left empty - the site will compare two empty values and allow you to pass the captcha. This method also does not always work, but it’s worth a try on a simple site without protection.

Besides all this, there are special programs for automatic captcha entry, they do not provide 100% captcha entry and allow quite a lot of errors, but in general they sometimes turn out to be very effective.

If you want to learn how to quickly enter captcha on your own, you will need a lot of training and patience. There are special sites where you can earn money by entering captchas - this is where the ability to quickly enter any captcha will be most useful to you.

For maximum input speed, try to ignore the presence of uppercase and lowercase letters in the captcha and enter all characters in small ones - the system most often counts such input. Also, don’t forget to use the numeric keypad, which makes entering numbers much faster.

Well, one of the most important tips is to learn “blind typing”. Try not to look at the keyboard when entering a captcha and your brain will gradually learn the location of all the keys, this will allow you to enter a captcha very quickly and almost automatically.

As you can see, bypassing captcha on the Internet is not easy, but you can always speed up this test. The main thing is to be patient and gain experience, because the more often you enter a captcha, the more you practice speed input.

I decided to take a short break from publishing about this PHP framework and switch to something else as an “active recreation”.

Therefore, I decided to talk to you about one very common cyber defense mechanism that allows you to prevent many automated attacks on websites and is used up to 320 million times daily today.

Can't guess what we'll talk about?

All of the above is about CAPTCHA, which probably 90% of all Internet users have seen and used, but, unfortunately, not everyone knows thoroughly what a captcha is and what problems it allows to solve.

What is captcha?

In search engines, a lot of people enter the query “CAPTCHA translation” every day. However, you will not find the correct answer to this question either in this or in other similar articles.

CAPTCHA is not just some specially made up term, but an abbreviation for the words Completely Automated Public Turing test to tell Computers and Humans Apart, which literally means “a fully automated public Turing test for recognizing computers and people.” Therefore, it is correct to write this word in capital letters.

In the Russian-speaking segment of the Internet it is often called “captcha”, because This is roughly how CAPTCHA is pronounced in Russian. The capital letters are omitted, which is why the history of the word “captcha” may be new to some readers, but it helps to trace the logical connection between it and the “automated Turing test.”

I think the decoding of the abbreviation itself perfectly explains what a CAPTCHA is. The only ambiguity may be the Turing test... If you think that at this point I will burden you with a bunch of formulas and definitions, then you are mistaken :)

I’ll tell you a few words about this as clearly as possible to broaden your horizons, otherwise you might come across a word in a crossword puzzle and you won’t know what it is :)

Once upon a time there lived (namely, at the beginning of the 20th century) an English mathematician named Alan Turing. The personality, by the way, is quite well-known in narrow circles, who came up with a lot of good things, for which they even started making films about him (this is exactly the guy played by Benedict Cumberbatch in the film “The Imitation Game”).

So, one day the thought “can a machine think?” came to his mind. Since Alan Turing was not a stupid person, as you may have noticed, the result of his thoughts was a test, the purpose of which is precisely to determine which of the interlocutors is a person and which is a computer.

The test was first described back in 1950 and was named in honor of its creator, by which it is known to this day - the Turing test.

The classic Turing test is a situation where a person (a judge) communicates with a computer and a real person text messages. If the judge cannot determine “xy from xy”, i.e. Which of the interlocutors is a human and which is a computer, then the machine is considered to have passed the test.

But it is wrong to think that it is very simple and easy to expose a computer :)

Various tricks are used to confuse the judge. First of all, myself text format communication, so that a person could not recognize a machine by voice or some other sign, and the computer could demonstrate its intelligence, and not the ability to recognize human speech (although, judging by today's videos with robots, these guys will soon have no problem with either , nor with the second).

In addition, messages from the person and the computer are sent at the same intervals so that the judge cannot find the computer based on the speed of its response.

But, despite all these tricks, already in 1966 (wow, “already” - 16 years later!) appeared computer program with the poetic name ELIZA, capable of passing this test. Many smart people still doubt whether the experiment with Eliza should be considered a Turing test or not, but the fact remains that the piece of hardware was able to confuse people.

So CAPTCHA is a modern Turing test that helps to weed out robots from people in automatic mode. Only the computer algorithm acts as a judge. Because of this, captcha is sometimes called a reverse Turing test.

And if you don’t pass this test, then by your actions you are saying that you are no different from a soulless robot, and sometimes even stupider when the latter was able to pass it :)

In addition, in some cases, with a certain number of unsuccessful attempts, you can still get banned by IP address on the site. I hope this will motivate you to be more responsible when entering captcha next time :)

By the way, despite the fact that the Turing test itself was invented in 1950, CAPTCHA is a fairly young phenomenon. Inventions similar to modern captcha appeared relatively recently - in 1997, and the term itself was coined in 2003.

I think now you understand what captcha is, how it appeared and when. The only question is “Why?” It’s a good question, so I won’t wait too long to answer :)

The question arises: why was it necessary to use CAPTCHA to determine who visited the site: a person or a robot?

The fact is that robots in the Internet world are special automated programs that are not always created to bring benefit. This could be the spread of spam, or even hacking of a resource.

By the way, even if you try to automatically guess passwords or send spam to unprotected sites, you can cause serious damage to them, creating a large load on the server, which will cause the site to stop working.

Therefore, the most important purpose of captcha is to ensure the security of the site by blocking attacks and performing automatic actions using various malicious programs.

Another answer to the question of why CAPTCHA is needed is the recognition of scanned books and other printed publications. How?

If you yourself have ever tried to digitize books yourself using Adobe FineReader or a similar program (I don’t know about you, but in my student years I often did this when writing essays and coursework 🙂), then you know that recognition is far from 100%.

This is despite the fact that most books are printed in standard printing font. For manuscripts, recognition by programs is practically zero.

So, the creators of CAPTCHA (in particular, the creators of Google reCAPTCHA) decided to take advantage of this circumstance. They composed words that were not recognized by the program, which were then displayed as captcha images asking real people to enter what they saw.

In this way, a database of options for decoding difficult-to-recognize words was collected and at the same time users proved that they were real people, because were able to recognize what they saw, which distinguishes us from robots. As for me, it’s brilliant, like everything else on Google, strictly speaking :)

The only point that remains unclear to me personally in this whole story is how did people pass the captcha with difficult to recognize characters, if for such there may even be several possible correct answers? Google, naturally, will not reveal its secrets.

But if I personally were developing this mechanism for text recognition by users using captcha, then I would select some more or less similar version of what is shown in the picture, so that it would be possible to check the user’s answer with it.

Or it would simply count the option entered by the user as an answer option, and would knowingly ask the user to enter the captcha again with a more readable sequence of characters for which there is an answer, so that the user would not think that he was being fooled and would not increase the number of incorrect attempts , for which they sometimes get banned.

By the way, I like the second option much better, because... with its help you can collect a database of correct user answers, having about 10 ready-made captchas with answers at the input. The rest will be collected automatically. All we need is to analyze and process user responses.

Thanks to all of the above, the creators of reCAPTCHA are promoting their project under the slogan “Stop spam - read books!” And I must say - it works :)

Today, thanks to gentlemen spam bots and their ilk, it is almost impossible to do anything online without entering characters from a generated image - CAPTCHA (hereinafter referred to as captcha). In fact, this prevents the execution of any script without human intervention, and in this topic I will tell you how to create such a captcha using PHP, and I will also mention a very useful topic from another Habrowser, which will be useful when developing a captcha image.

I warn you right away that the topic may be of interest only to novice developers, since in essence I am reinventing the wheel, but with my own hands.

Basic rules When developing a captcha, you must follow several basic rules:

1. Captcha was created for people
It should be immediately readable, but not at the expense of resistance to recognition. A very clear example of a captcha that does not comply with this rule is the image on the right.

2. The captcha generator must be clearly limited in the characters used
A good example is the image at the beginning of the topic. Of course, reCAPTCHA is a wonderful invention, but sometimes it prompts you to enter characters that are difficult to find in charmap. By the way, when it comes to captcha using Cyrillic characters, in no case should the generator use the letter “е”. Personally, I know a lot of people who have some action in their system assigned to ~ (tilde / e).

3. Captcha must be resistant to recognition
... but not at the expense of readability. In general, this point is the most difficult in the entire development. It is necessary to find a middle ground - the captcha is immediately read by people and generally (as far as possible) not read by bots. It is also necessary to take into account the specifics of the resource on which you plan to use the captcha, and its contingent. If we are talking about, say, a forum of reading housewives over forty, then you can spit on the durability of captcha from a high tower - it will not bother anyone. If we are talking about, for example, an imageboard, then you need a captcha a la vyrviglaz.

Design The theoretical object for which we will make a captcha will be a spherical forum in a vacuum, with moderately aggressive, moderately intelligent and generally moderate users. A very useful topic from Habrowser Pastafarianist will help us develop such a captcha. Namely, I will draw attention to the listed disadvantages and advantages of the captchas he took.

So, let’s list in order what we can use:

1. The image must use at least some colors. Always preferably different

The image above is an example of what this looks like in action. In fact, this is not a very reliable option, since the text contrasts very much with the background. We'll deal with flowers later.

2. There must be noise

The truism. In almost any captcha you can find noise, which is most often expressed in many lines crossing the text, of different lengths and at different angles.

3. Letters must be on a short distance apart from each other

The main thing here is not to overdo it. Excessive convergence of characters will lead to a severe deterioration in human readability. In the example above, you can see that the letters stick together, this creates an obstacle for the bot when segmenting the image.

4. Symbol sizes must be different

If you use this trick, you must remember that the obstacle is actually expressed in the fact that the bot will not be able to use a constant matrix to segment the captcha. Therefore, if you make the size of the symbols different, then for each symbol the size must be random, dynamic.

5. Ugly font

Very useful way. Serifs, italics, stylization are great pitfalls for a bot. Also, in combination with noise in the form of lines, a thin font will look very good. If we abstract from the first rule of captcha generation, then we can use many fonts at once, for example, a different font for each character.

6. Symbols at random angles

Very effective way protect yourself from bots. Again, segmentation will be more complicated, although not significantly. It is best to choose a small angle range, otherwise readability will be greatly affected (the letters will overlap each other).

7. Dynamic distortion

Humanity has not yet come up with anything more terrible. Distortions in captchas often greatly reduce human readability. Of course, this is quite effective against bots, but it is just as effective against people. The main thing is not to overdo it; distortions should be insignificant.

So what will we do:
- Contrasting background, with noise
- Lines behind the text, lines on the text
- Text in random position
- The number of symbols will be random, from 4 to 7
- The size of each symbol will be random
- Text color will be random each time
- The characters will touch lightly
- Each symbol will be at a random small angle

Development Let's decide on the goal:
- Noise generation
- Text generation
- Form with the ability to update captcha
- Processor of entered data
As I wrote the article, I realized that distortions in this case are absolutely inappropriate. For those who still need them, at the end of the topic is a link to a lesson on creating distortions. Write the form

Update captcha Enter captcha:
Everything is very clear here, but just in case, I commented on some lines. By the way, please note that I did not set the maxlenght parameter for the input field. In most cases, developers set this parameter by specifying the size of the captcha. Firstly, this is a pretty good hint for a bot, and secondly, the number of characters will be dynamic. That's it, we've written the interface, it's time to start creating a generation script. We're writing a captcha code generator (random.php)
Everything here is limited only by your imagination. Once I saw a different method - the current minute, hour, month were selected, all this was multiplied, and 10 were selected from this random symbols, the MD5 hash was extracted twice, 6 random characters were extracted from it, and then the whole thing was mixed. By the way, pay attention to the characters I chose - I excluded such as i, l, 1 and 0, o, c, due to the fact that they are too similar to each other, in some situations the user may make a mistake. I called the generator random.php (later it will be requested in other scripts). We write an image generator (captcha.php)