[PHP] some problems about gd in php

[zhaoxd]

I have installed gd-1.8.4 in apache server without any problems.To check if the gd can 
work,I write some codes in php like this:
<?
 Header("Content-type: image/png");
 $im = imagecreate(400,30);
 $black = ImageColorAllocate($im, 0,0,0);
 $white = ImageColorAllocate($im, 255,255,255);
 imageline($im, 1, 1, 350, 25, $black);
 imagearc($im, 200, 15, 20, 20, 35, 190, $white);
 imagestring($im, 5, 4, 10, "Graph TEST!!", $white);
 ImagePNG($im);
 ImageDestroy($im);
?>
But the result is warning message in IE:"<b>Warning</b>:  ImagePng: No PNG support in 
this PHP build in <b>/usr/local/apache/htdocs/index.php</b> on line <b>9</b><br>".

Is this a compiling problem?The compiling command of php is:

./configure --with-mysql=/usr/local/mysql --with-apache=../apache_1.3.24 
--enable-track-vars --with-gd=../gd-1.8.4 --with-png-dir=../libpng 
--with-zlib-dir=../zlib



Has something wrong or something I forgot?

Thank you.

                    zhaoxd