function checkClick(e){
  if(e && e.which && e.which == 3){
    alert("Copying images is prohibited.[1]");
    if(e.stopPropagation)
      e.stopPropagation();
    else
      e.cancelBubble = true;
    if(e.preventDefault)
      e.preventDefault();
    else
      e.returnValue = false;
  }
  else if(event.button && event.button == 2){
    alert("Copying images is prohibited.[2]");
  }
  return false;
}

function checkForMenu(e){
  var elem = e.target || e.srcElement;
  if(elem.tagName.toLowerCase() == 'img'){
    e.cancelBubble = true,
    e.returnValue = false;
    return false;
  }
  return true;
}

function checkContextMenu(e){
  var retVal = true;
  if(e)
    retVal = checkForMenu(e);
  else
    retVal = checkForMenu(event);
  return retVal;
} 

function checkImages(){
  for(var i = 0; i < document.images.length; i++) {
    document.images[i].onmousedown = checkClick;
  }
  document.oncontextmenu = checkContextMenu;
}