Trying to add a gallery…from a URL

I am updating my site w/ WP and am trying to add a gallery from an existing image folder on my main domain, but am not sure how to accomplish this.

I know I can upload all of my images all over again onto this subdomain, but I’d rather create galleries that link to my primary domain image folder rather than a subdomain image folder (which would double my server space).

Is there a simple way to do this? Can I browse to my public image folder and select a group of images for a gallery?

Thanks!