function on(imgId) {
	var strOver = "on-";
	var strOff = "off-";
	var img = document.getElementById(imgId);
	img.src = img.src.replace(strOff, strOver);
}

function off(imgId) {
	var strOver = "on-";
	var strOff = "off-";
	var img = document.getElementById(imgId);
	img.src = img.src.replace(strOver,strOff);
}