生成验证码函数

function MakePass($length){
    $possible = "0123456789".
    "abcdefghijklmnopqrstuvwxyz".
    "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    $str = "";
    while(strlen($str) < $length){
        $str .= substr($possible, (rand() % strlen($possible)), 1);
    }
    return($str);

}

调用

echo MakePass(5);
//生成5位验证码