var delay    = 40;
var factor   = 0.7;
var timer    = null;
var sliderEl = null;
var sliderLeft = 390;

function sliderInit() {
   var cell = document.getElementById('winterschilder');
   
   if (  cell
      && cell.firstChild.firstChild
      && cell.firstChild.firstChild.nodeType == 1
      && cell.firstChild.firstChild.tagName.toLowerCase() == 'img'
   ) {
      sliderEl = cell.firstChild.firstChild;
      setInterval('sliderUpdate();', delay );
   }
}

function sliderUpdate() {
   if (sliderEl.offsetLeft > sliderEl.offsetWidth * -1) {
      sliderEl.style.left = parseInt(sliderEl.offsetLeft - 1) + 'px';
   } else {
      sliderEl.style.left = sliderLeft + 'px';
      //clearInterval(timer);
   }
}

window.onload = sliderInit;