Someone

<?php
define('DIR', '../../img/font');
define('FONT_SIZE', 12);
define('SPACE_PIX', 20);
define('IMG_WIDTH', 500);
define('IMG_HEIGHT', 100);

$fonts = array();

// Indexing
if(is_dir(DIR)) {
  if($dh = opendir(DIR)) {
    while (($file = readdir($dh)) !== false)
      if(preg_match('/\.ttf$/', $file))
        $fonts[] = $file;

    closedir($dh);
  }
}

// Image Creating
if(in_array($_GET['f'].'.ttf', $fonts)) {
  $text = array('ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz', '123456789');

  header('Content-type: image/png');
    $img = imagecreate(IMG_WIDTH, IMG_HEIGHT);
      $bg = imagecolorallocate($img, 0xFF, 0xFF, 0xFF);
      $txt = imagecolorallocate($img, 0x00, 0x00, 0x00);

   imagettftext($img, FONT_SIZE, 0, 10 , 10, $txt, DIR.'/'.$_GET['f'].'.ttf', $text[0]);
   imagettftext($img, FONT_SIZE, 0, 10 , 10 + SPACE_PIX, $txt, DIR.'/'.$_GET['f'].'.ttf', $text[1]);
   imagettftext($img, FONT_SIZE, 0, 10 , 10 + SPACE_PIX + SPACE_PIX, $txt, DIR.'/'.$_GET['f'].'.ttf', $text[2]);

   imagepng($img);
   imagedestroy($img);
}
?>