PHP GD Library无法显示图片

Question

I have problem with PHP's GD Library..I've made this script for showing some users stats, and it can't work.I don't know why but it just shows broken picture..How can i fix it ?

Thanks, sorry for bad english

                     header("Content-type: image/png");

        $image      = imagecreatetruecolor(320, 180);

            $online_ico = imagecreatefrompng("/files/online.png");


            $avatar = imagecreatefrompng("/files/default.png");


        $white  = imagecolorallocate($image, 255, 240, 240);
        $green  = imagecolorallocate($image, 0, 255, 0);
        $red    = imagecolorallocate($image, 255, 0, 0);
        $blue   = imagecolorallocate($image, 9, 105, 162);

        $user_id = "25";
        imagefill($image, 0, 0, $blue); 

        //labels
        imagestring($image, 5, 20, 20, "ID ", $white);
        imagestring($image, 5, 20, 40, "UN", $white);
        imagestring($image, 5, 20, 60, "stats", $white);
        imagestring($image, 5, 20, 80, "name", $white);
        //data
        imagestring($image, 5, 130, 20, $user_id, $white);
        imagestring($image, 5, 150, 40, $user_id, $white);
        imagestring($image, 5, 130, 60, $user_id, $white);
        imagestring($image, 5, 130, 80, $user_id, $white);

        imagecopy($image, $online_ico, 130, 41, 0, 0, 16, 16);
        imagecopy($image, $avatar, 280, 140, 0, 0, 35, 35);

        imagepng($image);