I think that your requirement is not really what do you need. I guess that you really require quick loading of your web sites on the client browser. If I am false, you can stop your reading here :>)
My idea is very simple - you should dynamically resize the images on the server and cache them for next requests. Of course, the first user can be annoyed, but it is acceptable... Additionally, if the images repeats on the web, browsers will cache them.