How to make PHP verification code

PHP makes a verification code, mainly using array-related functions

<?php    Header ("Content-type:text/html;charset=utf-8");    Set up 3 range array    $shuzi = range (0,9);    $zimuda = Range (' A ', ' Z ');    $zimuxiao = Range (' A ', ' Z ');    Merge these 3 arrays into a new array    $arr =array_merge ($shuzi, $zimuxiao, $zimuda);    Iterate through the new array    foreach ($arr as $key + $value) {        //If the element in the new array contains the following word, delete it (unset); if        ($value = = ' 0 ' | | $value = = ') 1 ' | | $value = = ' 2 ' | | $value = = ' o '  | | $value = = ' O '             | | $value = = ' I ' | | $value = = ' I ' | | $value = = ' Z ' | | $value = = ' Z ' | | $value = = ' L ') {            //delete key, the value is also deleted            unset ($arr [$key]);}        }    The array element is scrambled, and its key value follows the element is disturbed    shuffle ($arr);    The 4 key values of the original array are randomly taken    $arr _rand = Array_rand ($arr, 4);    The key of the original array is traversed output to get 4 random verification Code    foreach ($arr _rand as $value) {        echo $arr [$value];    }    Optimization: 0,1,2 These 3 numbers originally need to exclude, just in the array of the first, continuous, in the definition of the range array can not write, directly from 3, reduce if judgment; uppercase and lowercase z can not be written at the end