I have two friends that want to create a jewelry store, focused on customized jewels. The core feature is the jewelry designer, based on a jewel model.

Here's an example of the sort of thing I am looking to create : http://www.gemvara.com/jewelry/wisteria-pendant/pear-citrine-18k-yellow-gold-pendant-with-diamond/155hhg

You can use the menu on the right to change different areas of the final image, such as the gems or metal used. If you right-click on the image, you can see it's a complete jpg.

How is this kind of dynamic image designed and programmed?