function stopEventPropagation(e) {
	if (!e) var e = window.event;
	e.cancelBubble = true;
	if (e.stopPropagation) e.stopPropagation();
};

function catchClick(e){
	var rightclick;

	//get event if ie
	if (!e) var e = window.event;

	//check for right click
	if (e.which) rightclick = (e.which == 3);
	else if (e.button) rightclick = (e.button == 2);

	//get target element
	if (e.target) var targ = e.target;
	else if (e.srcElement) var targ = e.srcElement;

	if(rightclick && targ.nodeName.toLowerCase()=='img'){
		alert("Protected content");
		if(e.preventDefault)e.preventDefault();
		stopEventPropagation(e);
		return false;
	}
}

document.onmousedown = function(e){
	//get event if ie
	if (!e) var e = window.event;

	//get target element
	if (e.target) var targ = e.target;
	else if (e.srcElement) var targ = e.srcElement;

	if(targ.nodeName.toLowerCase()=='img'){
		if(e.preventDefault)e.preventDefault();
		stopEventPropagation(e);
		return false;
	}
}

document.oncontextmenu = catchClick;
if(document.all)
	document.onmousedown = catchClick;