(function ($) {
$(window).ready(function() {
  var bgArray = ['header01-900x200.jpg','header02-900x200.jpg'];
  var bg = bgArray[Math.floor(Math.random() * bgArray.length)];
  var path = '/sites/default/files/images/';
  var imageUrl = path + bg;
  $('.not-logged-in .region.region-content').css({
   'background-image' : 'url(' + imageUrl +')',
   'background-repeat ' : 'no-repeat',
   'background-position-y' : '0'
});
});
})(jQuery);