GD library problem

[2005]

I just migrated to another server with PHP version 5.1.4.
All security images appear broken. When I call the script which generates security images, instead of image I get text:
http://myserver/sec_image.php

This is a part of my script:

...
$image = imagecreatefrompng("images/secimages/background.png"); 
$text_color = ImageColorAllocate($image, 80, 80, 80); 
Header("Content-type: image/png"); 
ImageString ($image, 5, 12, 2, $textstr, $text_color); 
Imagepng($image, '', 75); 

[NogDog]

Well, the obvious first question is: was the GD library enabled on the new server? (You can do a phpinfo() on a test page and check the "GD" portion of the output.)

[2005]

Yes, it's enabled.

[zabmilenko]

You have three arguments passed to imagepng(). Doesn't it only accept 2? Isn't the second supposed to be NULL if you don't want file output, not an empty string?