function show_image(thumb_id, id) {
	//replace thumb with what was in the main box
	var thumb = document.getElementById(id).src.replace(/main/, "thumb");
	var main = document.getElementById("thumb_"+thumb_id).src.replace(/thumb/, "main");
	//make the change
	document.getElementById("thumb_"+thumb_id).src = thumb;
	document.getElementById(id).src = main;
}