ho trovato tutto sul manuale online

codice:
<?php
  header("Content-type: image/jpeg");
  $im = imagecreate(400, 30);
  $white = imagecolorallocate($im, 255, 255, 255);
  $black = imagecolorallocate($im, 0, 0, 0);
  // Replace path by your own font path
  imagettftext($im, 20, 0, 10, 20, $black, "c:\windows\fonts\arial.ttf",
  "Testing... Omega:");
  $im=imagerotate($im,45,$white);
  imagejpeg($im);
  imagedestroy($im);
?>