function swappics() {

  pics = new Array("images/rotate1.jpg", "images/rotate2.jpg", "images/rotate3.jpg", "images/rotate4.jpg");
  var randpic = Math.floor(Math.random() * (4));

  document.randompic.src = pics[randpic];
  intervalID = setInterval(changeit, 4000)

}


function changeit() {

  var randpic = Math.floor(Math.random() * (4));
  document.randompic.src = pics[randpic];

}