As suggested in http://forum.opencart.com/viewtopic.php?f=138&t=40573 I'm trying to use a subdomain for the images to speed up the site
I created a subdomain images.mywebsite.com pointing to mywebsite.com/image and it works as I can see the file images.mywebsite.com/no_image.jpg on the browser.

On a 1.5.6.1 installation, my config.php and admin/config.php don't have any define HTTP_IMAGE, but I have the define DIR_IMAGE
define('DIR_IMAGE', '/home4/bartolo/public_html/mywebsite.com/image/');
if I change it to
define('DIR_IMAGE', 'http://images.mywebsite.com/');
it does not show any images (even if I F5 refresh).
How should it be done on 1.5.6.1?
Thanks in advance,
Pak