How to implement verification code function in php

PHP implements the verification code function through the GD library, combined with examples to analyze the PHP verification code related image drawing and output operation implementation techniques. Share it with everyone for your reference, the details are as follows:

First look at the effect achieved: (recommended learning: PHP video Tutorial)

Specific implementation:

To realize the connection of forms and the "change one" function Implementation: 



" alt="验证码">

换一个 
captcha.php is followed by a random parameter to achieve the function of changing a verification code. Changing the function can be achieved through simple js. If there is no such function, no parameters can be used. 
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