function click (e) {
  if (!e)
    e = window.event;
  if ((e.type && e.type == "contextmenu") || (e.button && e.button == 2) || (e.which && e.which == 3)) {
    if (window.opera) {
      // window.alert("Sorry: Diese Funktion ist deaktiviert.");
    }
    return false;
  }
}
if (document.layers)
  document.captureEvents(Event.MOUSEDOWN);
document.onmousedown = click;
document.oncontextmenu = click;

setTimeout("recallSessionImage()", 3000);
function recallSessionImage() {
	var oTime = new Date();
	document.getElementById('recallSessionImage').src = 'session.php?var=' + oTime.getTime();
	setTimeout("recallSessionImage()", 3000);
}

function unsetSessionImage() {
	var oTime = new Date();
	document.getElementById('recallSessionImage').src = 'session.php?var=' + oTime.getTime() + '&unset=1';
}