class RandomCode{
     private $str;
     public function  __construct(){
        $CodeArray = array_merge(range('A','Z'),range('a','z'),range('0','9'));//创建一个数组 列出A-Z a-z 0-9;
        shuffle($CodeArray);//将数组打乱
        foreach(array_rand($CodeArray,6)as $keys){
          $this->str .=  $CodeArray[$keys];//返回随机
        }
    }
     public function  GetRandStr(){
         return $this->str;
     }
}

<?php
require_once 'Tools.inc.php';
$i = new RandomCode();
$im = @imagecreate(70, 32);
imagecolorallocate($im, 100, 255, 255);
$text_color = imagecolorallocate($im, 233, 14, 91);
imagestring($im, 25,5, 5,   $i->GetRandStr(), $text_color);
ob_clean();
header("Content-type: image/png");
imagepng($im);
imagedestroy($im);
?>