New Post: Product Image Change

That's not something I can give you a full solution for here. But probably the easiest solution would be to place some JQuery in the display templates which is triggered by a change event on the dropdowns..

http://api.jquery.com/change/

You'll need to give each image you have a class to identify then and then hide or show them based on the dropdown change event.

http://api.jquery.com/hide/
http://api.jquery.com/show/