$im = imagecreatefromgif('trans.gif');
$img = imagecreatetruecolor(16,16);
imagecopymerge($img,$im,0,0,0,0,16,16,100);
imagecolortransparent($img, imagecolorallocate($img,255,99,140));
imagegif($img,'trans.gif');
imagedestroy($img);