Alternative to captcha.

Instead of forcing a person to prove that he is not a robot, you can try to force the car to reveal itself.

Damien Katz suggested doing it with CSS.
To do this, he says, you need to use the email input field, hidden from the user by means of CSS.

When a person completes a form, he cannot fill a hidden field, it will be empty. But, if the bot fills the form, it will insert some text into this field (he will not know that this field is hidden) and add it.
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Thus, if among the data sent by the form is this email, the form was sent by the bot.