I believe that images on the same domain can contribute to search engine rankings (mainly Google), example:
So it is my understanding that using a images on a different domain or a (CDN) content delivery network is not good for SEO. A popular solution is to use a sub domain, such as:
- Does hosting images on a sub domain impact SEO?
- Does hosting images on a different domain impact SEO?
- Does hosting images on a CDN impact SEO?