window.onload = function () {
    var header = document.getElementById('headerhome');
    var pictures = new Array('http://goodoakllc.com/images/shell/homea.jpg','http://goodoakllc.com/images/shell/homeb.jpg','http://goodoakllc.com/images/shell/homec.jpg');
    var numPics = pictures.length;
    if (document.images) {
        var chosenPic = Math.floor((Math.random() * numPics));
        header.style.background = 'url(' + pictures[chosenPic] + ') no-repeat bottom';
    }
}



function addLoadEvent(func) {
  var oldonload = window.onload;
  if (typeof window.onload != 'function') {
    window.onload = func;
  } else {
    window.onload = function() {
      if (oldonload) {
        oldonload();
      }
      func();
    }
  }
}

addLoadEvent(changeHeader);