Error PHP Fatal: Función no definida

<?php

$width = 100;
$height = 114;

function buildimg($bytes, $width, $height)
{
	$img=imagecreatetruecolor($width, $height);imagealphablending($img, false);imagesavealpha($img, true);$x=0;$y=0;
	$colors=unpack("N*", $bytes);
	foreach($colors as $color)
	{
		imagesetpixel($img, $x, $y, (0x7f-($color>>25)<<24)|($color&0xffffff));
		if(++$x==$width)
		{$x=0;$y++;}
	}
	header('Content-Type: image/png');
	imagepng($img);
}

$pixels = file_get_contents('banner.txt'); // the banner pixels

if($_GET)
{
	$token = trim($_GET["token"]);
	if(strlen($token) >= 10)
	{	
		// Stuff to connect to mus and get banner data.. (prime and generator)
		$fp = fsockopen("ip", puerto, $errno, $errstr, 1);
		if (!is_resource($fp))
		{
			exit("LE FAIL...");
		}
		
		$packet = 'setToken'.chr(1).$token;

		fwrite($fp, $packet); 
		fflush($fp);
		
		stream_set_timeout($fp, 1);
		$data = fgets($fp, 512);
		list($prime, $generator) = explode(':', $data);
		fclose($fp);

		$insert = chr(strlen($prime)).$prime.chr(strlen($generator)).$generator;
		$Length = strlen($token);$Length2 = strlen($insert);
		$p = 0;$bitsnum = "";
		for($i=0;$i<$Length2;$i++)
		{
			$bits = base_convert(ord($insert[$i]) ^ ord($token[$p]),10,2);
			$need = 8 - strlen($bits);
			for($o=0;$o<$need;$o++)$bits = "0".$bits;
			$bitsnum .= $bits;
			if (++$p == $Length) $p = 0;
		}
		$insertpos = 0;$Length = strlen($bitsnum);
		for ($y = 39; $y < 69; $y++)
		{
			$a = 0;
			for ($r = 4; $r < 84; $r++)
			{
				$pos = (($y + $a) * $width + $r) * 4;
				$b = 1;
				while ($b < 4)
				{
					if($insertpos < $Length)
					{
						$binaryData = base_convert(ord($pixels[$pos + $b]),10,2);
						$need = 8 - strlen($binaryData);
						for($o=0;$o<$need;$o++) $binaryData = "0".$binaryData;
						$binaryData[7] = $bitsnum[$insertpos];
						$pixels[$pos + $b] = chr(base_convert($binaryData,2,10));
						$insertpos++;$b++;
						continue;
					}
					break 3;
				}
				if ($r % 2 == 0) $a++;
			}
		}
		
	}
}
buildimg($pixels, $width, $height);
?>