imagettfbbox = undefined function?

I just downloaded a script, and part of that script is this file:


<?php

/*

Nice script from http://www.finalwebsites.com/snippets.php?id=39

example of usage:
inside your form
<input type="text" name="validator" id="validator" size="4" />
<img src="captcha.php" alt="CAPTCHA image" width="60" height="20" vspace="1" align="top" />

and test the value of the "validator" form field like:
if (!empty($_POST['validator']) && $_POST['validator'] == $_SESSION['rand_code']) {
process your form here
at least destroy the session
unset($_SESSION['rand_code']);

*/

session_start();
session_regenerate_id(true); // Generate new session id and delete old (PHP >= 5 only)

// Captcha string
if (!isset($_SESSION['rand_code'])) {
$str = "";
$length = 0;
for ($i = 0; $i < 4; $i++) {
// this numbers refer to numbers of the ascii table (small-caps)
$str .= chr(rand(97, 122));
}
$_SESSION['rand_code'] = $str;
}

// generate captcha image
$imgX = 60;
$imgY = 20;
$image = imagecreatetruecolor(60, 20);
$backgr_col = imagecolorallocate($image, 238,239,239);
$border_col = imagecolorallocate($image, 125,125,125);
$text_col = imagecolorallocate($image, 125,125,125);
imagefilledrectangle($image, 0, 0, 60, 20, $backgr_col);
imagerectangle($image, 0, 0, 59, 19, $border_col);
$font = "includes/elephant.ttf"; // font
$font_size = rand(12, 15);
$angle = rand(-5, 5);
//Line 46 VVV
$box = imagettfbbox($font_size, $angle, $font, $_SESSION['rand_code']);
//Line 46 ^^^
$x = (int)($imgX - $box[4]) / 2;
$y = (int)($imgY - $box[5]) / 2;
imagettftext($image, $font_size, $angle, $x, $y, $text_col, $font, $_SESSION['rand_code']);
header("Content-type: image/png");
imagepng($image);
imagedestroy ($image);

?>



When that is run, I get
Fatal error: Call to undefined function: imagettfbbox() in /home/dotbooks/public_html/auth/captcha.php on line 46


PHP version 4.4.3

GD info:

gd
GD Support enabled
GD Version bundled (2.0.28 compatible)
GIF Read Support enabled
GIF Create Support enabled
JPG Support enabled
PNG Support enabled
WBMP Support enabled
XBM Support enabled

What's going wrong?

you need Freetype as well as GD