What kind of captcha can there be for a website?

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Security code

A captcha in the form of a security code is a fuzzy, crossed-out letter or number. It can be easy or difficult to recognize. Simple captchas are passed by bots, and difficult ones are difficult to recognize even for a person.

Depending on the level of complexity, captchas dj email list are:

very simple (clear, single-color numbers or letters);

simple (colored symbols without noise);

medium (colored symbols with overlay lines and noise);

high (characters with slant, obvious lines and noise);

very high (characters with tilt, strong noise and blocks).

Very simple and simple captchas are not an obstacle for bots. Robots will definitely not be able to reproduce captchas of very high complexity, but not every user can see and understand such symbols. Therefore, it is optimal to put a captcha of medium or high complexity on the site.

A simple question or math problem

A captcha in the form of a question or task is necessary to confirm that the user is a human. There may be several questions and tasks. The user will complete the task, but a robot will not be able to, because it cannot reason or think. Therefore, this type of captcha is considered the most reliable. Programs that can pass this captcha exist in nature, but there are very few of them. In any case, no one has canceled manual site verification, as well as spam cleaning.

A simple question or math problem

Logical problem

Captcha in the form of a logical task is also difficult for most robots. Answering a logical question is much more difficult than solving a simple mathematical problem.

Especially when the tasks are tricky, for example:

what is the eighth letter in the word "abracadabra";

write the number "forty seven thousand four hundred sixty seven four" in digits;

Write the largest number from 2, forty three, 80, 56, 65.

For many, solving a logical problem is even easier than reproducing a complex captcha with noise. This is precisely the positive side of using this type of tasks. However, finding an answer to a number of questions will take time, since the wording may be unusual. Plus, some bots will still be able to bypass this obstacle.

Checkbox

A captcha in the form of a checkbox, that is, a regular tick that needs to be put, is convenient for users, saves their time and nerves. However, it can also become a problem for people with poor eyesight, who simply will not notice it.

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Graphic captcha

A graphic captcha is a task to find some objects in a picture. There are many types of such tasks. For example, it is suggested to mark all the squares where there are road signs, bridges, buses, etc. For people, such tasks are not difficult, but a program can stumble on them.

Graphic captcha

Personality recognition

A version of captcha in the form of recognizing friends' faces from a user's profile was first proposed by Facebook back in 2011. However, this solution did not become popular. There are two global reasons. First, a person does not always know their online friends personally. This is especially true for celebrities who have a lot of fans among their friends. Second, it is difficult even for police officers and FSB officers to reliably identify a person from a photo, since in the modern world, people's appearance in photos and in real life sometimes differs dramatically.