How to make a PHP verification code

PHP creates a verification code, mainly using array related functions

<?php
    header("content-type:text/html;charset=UTF-8");
    //建立3个范围数组
    $shuzi = range(0,9);
    $zimuda = range(&#39;A&#39;,&#39;Z&#39;);
    $zimuxiao = range(&#39;a&#39;,&#39;z &#39;);

    //将这3个数组合并成新数组
    $arr=array_merge($shuzi,$zimuxiao,$zimuda);

    //遍历新数组
    foreach ($arr as $key => $value) {
        //如果新数组里的元素包含下面的字，则将其删除（unset）；
        if($value == &#39;0&#39; || $value == &#39;1&#39; ||$value == &#39;2&#39; ||$value == &#39;o&#39;  ||$value == &#39;O&#39; 
            ||$value == &#39;I&#39; ||$value == &#39;i&#39; ||$value == &#39;Z&#39; ||$value == &#39;z&#39; ||$value == &#39;l&#39;){
            //删除键，值也随之删除
            unset ($arr[$key]);
            }
        }

    //将数组 元素打乱，其KEY值跟随元素被打乱
    shuffle($arr);
    //随机取出原数组的4个key值
    $arr_rand = array_rand($arr,4);
    //将原数组的key遍历输出，得到4个随机验证码
    foreach ($arr_rand as $value) {
        echo $arr[$value];
    }

    //优化一下：0,1,2这3个数原本就需要排除，刚好在数组最前、连续，在定义范围数组的时候可以不写，直接从3开始，减少if判断；大小写字母Z在最后也可以不写

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