I don't know the right term for this but I have seen it.

On my community tourism site I have many images, all 200px x 150px or close.

Far too small now.

I want to show, on a click on the image, an identical, larger, preloaded image (say 500px wide) which partially covers the page. Click on that, back to the smaller image.

This is possible, yes? And it's done by JavaScript acting on the DOM?

So what is the term for this and where are the resources? (Know the last will be problematic!)