<?php
session_start();
function show_image()
{
    $Rastgele=rand(0,999999999);
    $Kod=md5($Rastgele);
    $Guvenlik=substr($Kod,-10);
    $_SESSION['Guvenlik']=$Guvenlik;
    $Width=100;$Height=25;
    $Resim=imagecreate($Width,$Height);
    $Beyaz=imagecolorallocate($Resim,255,255,255);
    $Siyah=imagecolorallocate($Resim,0,0,0);
    imagefill($Resim,0,0,$Siyah);
    imagestring($Resim,5,5,5,$_SESSION[Guvenlik],$Beyaz);
    header("Content-Type:image/png");
    imagepng($Resim);
    imagedestroy($Resim);
    exit;
}

if (isset($_GET['show_image']) OR isset($_REQUEST['show_image']))
{
    show_image();
}
elseif ($_SERVER['REQUEST_METHOD'] == 'POST')
{
    $code = trim($_POST['code']);
    $error = false;
    if (empty($code) OR $code != $_SESSION['Guvenlik'])
    {
        $error = true;
    }
    else
    {
        echo '<script type="text/javascript">alert("Dogru kod.. yonlendirileceksiniz...");</script>';
        //header("Location: xxxx.php");
        exit;
    }
}

echo '
<script type="text/javascript">
    function reload ()
    {
        document.getElementById(\'guvenlikkodu\').src = "'.$_SERVER['SCRIPT_NAME'].'?" + (new Date()).getTime() + "&show_image=1";
        return;
    };
</script>
<br><img src="https://www.r10.net/php/'.$_SERVER['SCRIPT_NAME'].'?show_image=1" border="0" id="guvenlikkodu" style="cursor:pointer" onclick="javascript:reload()" alt="okumakta zorluk cekiyorsaniz buraya tiklayin" title="okumakta zorluk cekiyorsaniz buraya tiklayin"><br>';
echo '<form method="POST" action="'.$_SERVER['SCRIPT_NAME'].'">
Guvenlik kodunu girin: <input type="text" name="code" value="">
<input type="submit" value="dogrula"></form>'.($error ? '<br><br><b>Hatali kod.</b>' : '');
?>