Here's the answer for your 256 color only problem!!!
use these functions in order then it works fine!

$img_src=imagecreatefromjpeg('yoursource.jpg');
$img_dst=imagecreatetruecolor(20,20);
imagecopyresampled($img_dst, $img_src, 0, 0, 0, 0, 20, 20, 20, 20);
imagejpeg($img_dst, $g_dstfile, 100);
imagedestroy($img_dst);

Greetz, GTB
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Manual Page -- [url]http://www.php.net/manual/en/function.imagecreatefromjpeg.php[/url]
Edit Note -- [url]http://master.php.net/manage/user-notes.php?action=edit+33821[/url]
Delete Note -- [url]http://master.php.net/manage/user-notes.php?action=delete+33821&report=yes[/url]
Reject Note -- [url]http://master.php.net/manage/user-notes.php?action=reject+33821&report=yes[/url]