Help with TTF font please

[Patriot]

The following code:

$banner     = imagecreatefromgif("backgrounds/sigt" . rand(1,6) . ".gif");
	$prizeimage = imagecreatefromgif("prizes/ps3.gif");

	$fontcolor  = imagecolorallocate($banner, 0, 0, 0);
	imagettftext($banner, 13, 0, 7, 73, $fontcolor, "MyriadPro-Regular.otf", "Freebie: " . $prize);

	imagecopy($banner, $prizeimage, 312, 4, 0, 0, 84, 97);

 

Selects a random background and writes text on it.  While the text should be black, it is becoming partially transparent on some backgrounds, making it gray or almost invisible.  Does anyone know why this is?

 

Thanks!