How to make two domains for one site?

Question

Domain name market

Hello.
The essence of the question is this, there is a site with the site.com domain. There was a need to use the domain exampe.com.
There were posts on the site (forum) where people shared photos from photo hosting (img.site.com). It is necessary that when changing the domain to example.com, pictures from the photo hosting work.

Answer 1

On the second hosting, put a simple script that will redirect the request to the main site with the same parameters.
Or make a complete copy of the site, then you get a mirror.