Note: I have commented some basic codes. The number of verification code digits and the required strings implemented here can be set again. With my annotations, it should be easy for everyone to understand.

Basic idea:

1. Use mt_rand() to randomly generate numbers to determine the string to be obtained, and splice the strings (I think the generated verification code is a bit too crowded, you can splice a space bar in the middle of the string) , to implement random verification code;

Note: It is recommended that you use mt_rand() instead of rand(), the former is more efficient

2. Use the gd library to generate pictures and write random strings to the picture output.

Effect:

Every time it is refreshed, a random verification is generated. Later I may add how to implement the random code and click on the picture to update again

Code:

<?php
// 創(chuàng)建畫布
$width = 120;   // 規(guī)定畫布的寬高
$height = 45;
$image = imagecreatetruecolor($width, $height);  // 創(chuàng)建一幅真彩色圖像
// 添加一些即將用到的顏色
$white = imagecolorallocate($image, 0xf2, 0xec, 0xe0);
$orange = imagecolorallocate($image, 0xff, 0xa5, 0x4c);
// 對畫布背景填充顏色
imagefill($image, 0, 0, $white);

//mt_rand  獲取隨機數(shù) mt_rand(min, max);
    function  str_rand(){
        $str="abcdefghijkmnpqrstuvwxyz0123456789ABCDEFGHIGKLMNPQRSTUVWXYZ";
        $rand="";
        for($i=0; $i<5; $i++){//獲取5個隨機的字符串
            $rand .= $str[mt_rand(0, strlen($str)-1)];  //如：隨機數(shù)為30  則：$str[30]
        }
        return $rand;
    }
$verifyCode=str_rand();
// 畫一串字符串在畫布上
imagestring($image, 10, 10, 10, "$verifyCode", $orange);
// 通知瀏覽器輸出的是圖像（png類型）
header(&#39;Content-Type: image/png&#39;);
// 輸出到瀏覽器
imagepng($image);
// 釋放圖像資源