Duplicating dynamically loaded image...ahhh

Hi guys. I need help…

I’m building an image gallery which creates thumbnails by sizing down the original images and once you click on one of them it duplicates itself and displays on top with full scale. I searched the web and everybody say duplicating dynamically loaded image can not be done and only solution is to reload the image. And because they are cached when they were first loaded it shouldn’t take much time to get loaded. Also I heard that there is way to force the browser to cathe the image… which I don’t know how.
Is this the only solution? I need help guys…