The problem of malicious registration of PHP webpage by SMS

Now there is a way to identify the verification code. You can quickly read the verification code content and then fill it in automatically, so you can still register maliciously. You can limit the number of daily registrations for a single IP. Or use a mobile phone number to add an SMS verification code, and limit the number of times the same mobile phone number can get verification codes per day, as well as the number of incorrect verification codes. When the limit is reached, it will be added to the blacklist. You can also use complex verification codes like Baidu Tieba, which is the one that selects category pictures.