Page load different background http://stackoverflow.com/questions/12115883/onload-javascript-assign-background-image-to-div

random-background.js

$(window).load(function(){
  var images = ['bg1', 'bg2', 'bg3'];
	var imageRandom = Math.floor( Math.random() * images.length );
	var imagesUrl = 'url(../img/' + images[imageRandom] + '.jpg)';
	$('body').css('background-image', imagesUrl);
});