Creare immagine png dinamica con stat forum

[Doc90]

Come da titolo...

Non so quasi niente di php ma ho trovato uno script per creare (in teoria) un'immagine dinamica con le statistiche del forum che si aggiorni, diciamo, in tempo reale...

Lo script è questo:

<?php

global $lang, $cache;

$lang->load('stats');

$stats = $cache->read('stats');

$img_width = 468;
$img_height = 30;

$border_color_outer = '#000000';
$border_color_inner = '#ffffff';

$gradient_start = '#035488';
$gradient_end = '#026cb1';

$color_top = '#ffffff';
$color_bottom = '#fff6bf';

$custom_text = false;

$im = imagecreatetruecolor($img_width, $img_height);

$gradient_start = hex2rgb($gradient_start);
$gradient_end = hex2rgb($gradient_end);

for($i = 0; $i < $img_height; $i++)
{
	$line_color = imagecolorallocate($im, max(0, $gradient_start['r']-((($gradient_end['r']-$gradient_start['r'])/-$img_height)*$i)), max(0, $gradient_start['g']-((($gradient_end['g']-$gradient_start['g'])/-$img_height)*$i)), max(0, $gradient_start['b']-((($gradient_end['b']-$gradient_start['b'])/-$img_height)*$i)));
	imageline($im, 0, $i, $img_width, $i, $line_color);
}

if($border_color_outer)
{
	$border_color_outer = hex2rgb($border_color_outer);
	$border_color_outer = imagecolorallocate($im, $border_color_outer['r'], $border_color_outer['g'], $border_color_outer['b']);
	imagerectangle($im, 0, 0, $img_width-1, $img_height-1, $border_color_outer);
}

if($border_color_inner)
{
	$border_color_inner = hex2rgb($border_color_inner);
	$border_color_inner = imagecolorallocate($im, $border_color_inner['r'], $border_color_inner['g'], $border_color_inner['b']);
	imagerectangle($im, 1, 1, $img_width-2, $img_height-2, $border_color_inner);
}

$color_top = hex2rgb($color_top);
$color_top = imagecolorallocate($im, $color_top['r'], $color_top['g'], $color_top['b']);

$color_bottom = hex2rgb($color_bottom);
$color_bottom = imagecolorallocate($im, $color_bottom['r'], $color_bottom['g'], $color_bottom['b']);

$string_top = $mybb->settings['bbname'];

if($custom_text)
{
	$string_top .= ' - '.$custom_text;
}
else
{
	$string_top .= ' - '.$mybb->settings['bburl'];
}

$string_bottom_users = $lang->members.' '.$stats['numusers'];
$string_bottom_posts = $lang->posts.' '.$stats['numposts'];
$string_bottom_threads = $lang->threads.' '.$stats['numthreads'];

$padding_lr = 10;

imagestring($im, 3, $padding_lr, 2, utf8_decode($string_top), $color_top);
imagestring($im, 2, $padding_lr, 14, utf8_decode($string_bottom_users), $color_bottom);
imagestring($im, 2, intval(($img_width-2*$padding_lr)/3), 14, utf8_decode($string_bottom_posts), $color_bottom);
imagestring($im, 2, intval(($img_width-2*$padding_lr)/3*2), 14, utf8_decode($string_bottom_threads), $color_bottom);

header('Content-type: image/png');
header('Content-disposition: inline; filename="'.$mybb->settings['bbname'].'.png"');

imagepng($im);
imagedestroy($im);

function hex2rgb($hex)
{
	$hex = ltrim($hex, '#');
	$rgb['r'] = hexdec(substr($hex, 0, 2));
	$rgb['g'] = hexdec(substr($hex, 2, 2));
	$rgb['b'] = hexdec(substr($hex, 4));
	return $rgb;
}

?>

io l'ho copiato in un file.php e l'ho inserito nella root del forum, ma quando provo a chiamarlo mi restituisce questo errore:
Fatal error: Call to a member function on a non-object in /membri/nerdnest/forum/sig.php on line 5

il forum è su piattaforma mybb