//variable that will increment through the images
var step=1;
function backimg(content) {
	document.getElementById(content).style.backgroundImage="url('images/site/"+step+".jpg')"; 
	if (step<6) {
		step++;
	}
	else {
		step=1;
	}
}

//add this command to where you would like thie images to loop through
setInterval ( "backimg('contenthome')", 3000 );