I am wondering about a few things here. First, what is the purpose of having an overlaid image and using the image maps? I see you're including jQuery - can you use the hover event with jQuery to change the orientation of the images and do the swap? What about attaching to the click event for the image map, and checking to see if the lightbox is open. If it is, then return false;
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Just trying to think out loud. Sometimes another take on it can be helpful.