$('document').ready(function(){
	var curr_button_is_on;
	$('img.nav-button').mouseover(function(evtObj){
		var button = evtObj.target;
		curr_button_is_on = $(button).hasClass('on');
		button.src = button.src.replace(/-off/, '-on');
		evtObj.stopPropagation();
	}).mouseout(function(evtObj){
		var button = evtObj.target;
		if (!curr_button_is_on) button.src = button.src.replace(/-on/, '-off');
		evtObj.stopPropagation();
	});
});