How to setup multiple subdomain image?

How to setup multiple sub domain image?

from below link i no idea to create it
http://forum.opencart.com/viewtopic.php?f=23&t=8492
at present i can sub domain only 1 for image
i want it 2, 3 because i have many products in sites

the reason is for loading speed page
because i have many images

You should not need to do that.

As long as the images are served from a different domain or subdomain (CDN) to that of the scripting etc then it should be fine.

so
if my subdomain like this one should be fine?

img.myshop.com<<--- store img
myshop.com <<--- oc shop

or this is better
img1.myshop.com <<< --- store img for catalog1
img2.myshop.com <<< --- store img for catalog2
myshop.com <<--- oc shop

??

You first solution should work fine