var returnFalse = new Function ("return false");
var returnTrue = new Function("return true");
function checkImage(e) {
if (document.all) {
    if ("IMG" == event.srcElement.tagName) return false;
  } else if (document.getElementById) {
    if ("IMG" == e.target.tagName) return false;
  }
}
if(document.layers) {
   window.captureEvents(Event.MOUSEDOWN);
  window.onmousedown = function(e) {
    if(e.target==document || e.which == 3) return false;
  }
} else if (document.all) {
   document.oncontextmenu = checkImage;
  document.onselectstart= returnFalse;
}