How to load a JPEG image and make the background transparent?

[HaLo2FrEeEk]

I've got an image that I want to load, it's a JPEG image and it has a solid background of color rgb(11, 12, 14). I want to make the background transparent and outpt the image as a PNG. I've tried this code:

header("Content-Type: image/png");
$im = imagecreatefromjpeg("http://www.bungie.net/stats/reach/nightmap.ashx");
$bg = imagecolorallocate($im, 11, 12, 14);
imagesavealpha($im, true);
imagecolortransparent($im, $bg);
imagepng($im);

It didn't work. I thought I knew why, too. JPEG images are palette based not true color, so they can't have transparency. I tried changing my code to this:

header("Content-Type: image/png");
$jpeg = imagecreatefromjpeg("http://www.bungie.net/stats/reach/nightmap.ashx");
$im = imagecreatetruecolor(imagesx($jpeg), imagesy($jpeg));
imagecopymerge($im, $jpeg, 0, 0, 0, 0, imagesx($jpeg), imagesy($jpeg), 100);
imagedestroy($jpeg);
$bg = imagecolorallocate($im, 11, 12, 14);
imagesavealpha($im, true);
imagecolortransparent($im, $bg);
imagepng($im);

Creating a truecolor image and copying my JPEG image to it, then operating on the truecolor image. Still didn't work.

Anyone have any ideas as to how I might get this to work, preferably without using a mask.