Cache externally linked image?

Is it possible to have an externally linked image and have it remain loaded so that it doesn’t have a minor pause before appearing if you click off the page then go back to it?

I creating a product page and want to use external links to keep file size down and not sure how best to do this since each range will have a different background and I’d like it to be as smooth as possible to go between them… perhaps even a slight fade in and out?!