function rand(n) {
  return Math.floor(Math.random() * n * 0.999)
}

var timer = 1500;

function wissel() {
  var v = document.getElementById('vakjes');
  var img = v.getElementsByTagName('IMG');
  var idea = [];
  for (var i=0; i<img.length; i++) {
//    if (img[i].className == "idea")
      idea.push(img[i]);
  }
  var n1 = rand(idea.length);
  var n2 = rand(img.length);
  var s1 = idea[n1].src;
  idea[n1].src = img[n2].src;
  img[n2].src = s1;

  /*
  timer -= 200;
  if (timer < 300)
    timer = 300;
  */
  setTimeout(wissel, timer);
}

function init() {
//  wissel();
  setTimeout(wissel, 1000);
}

onload = init;