function swap_images(element) {
	existing=$(element).children().attr('src');
	if (existing.substr((existing.length-7))=='-on.png') {
		replacement=existing.replace(/-on.png/, '-off.png');	
		$(element).children().attr('src', replacement);
	} else {
		replacement=existing.replace(/-off.png/, '-on.png');	
		$(element).children().attr('src', replacement);
	}
}