Where are the images coming from? A site you're authorized to hotlink images from? If not, most people don't take too kindly to wasting their bandwidth.
Many websites use hotlink protection, and some even serve inappropriate images to any unauthorized website hotlinking. Not a good idea.
If you're not talking about hotlinking, check out the Image Teleporter plugin. Although copyright is a concern, so make sure you have the rights to use the images.