PHP convert text to image

header("Content-type: image/png");
$string = $_GET['text'];
$im = imagecreatefrompng("images/button.png");
$color = imagecolorallocate($im, 255, 255, 255);
$px = (imagesx($im) - 7.5 * strlen($string)) / 2;
$py = 9;
$fontSize = 1;
imagestring($im, fontSize, $px, $py, $string, $color);
imagepng($im);
imagedestroy($im);
?>

转换成, PHP