// Random Image Background
var numImages = 4;
var ranNum = Math.floor( Math.random() * numImages ) + 1;
var img = '/theme_photos/photo-' + ranNum + '.jpg';

function setImage(img) {
  var objBG = document.getElementById( 'ranBG' );
  objBG.setAttribute( 'background', img );
}
setImage(img);