Simple Drag&Drop with JavaScript, JQuery

<script language="JavaScript">
	var mouseDown = false;
	var clonedElm = null;
	var xOffset = 0, yOffset = 0;

	$().ready(function(){
		$(document).mousedown(onMouseDown);
		$(document).mousemove(onMouseMove);
		$(document).mouseup(onMouseUp);
	});

	function onMouseDown (event)
	{
		if (event.srcElement == undefined && event.target != undefined)
			event.srcElement = event.target;

		if (!$(event.srcElement).hasClass("rk_draggable"))
			return;

		mouseDown = true;

		if ($(event.srcElement).hasClass("rk_clonable"))
		{
			//clone the element
			clonedElm = $(event.srcElement).clone();
			$(clonedElm).removeClass("rk_clonable");
			$(clonedElm).addClass("rk_thumbnail");
			var offset = $(event.srcElement).offset();
			$(event.srcElement).parent().append($(clonedElm));
			$(clonedElm).offset(offset);
		}
		else
		{
			clonedElm = $(event.srcElement);
		}

		var tmpOffset = clonedElm.offset();
		xOffset = tmpOffset.left - event.pageX;
		yOffset = tmpOffset.top - event.pageY;

		$(clonedElm).css("position", "absolute");

		var width = $(event.srcElement).width();
		var height = $(event.srcElement).height();

		$(clonedElm).width(width);
		$(clonedElm).height(height);

		return false;
	}

	function onMouseMove (event)
	{
		if (clonedElm == null)
			return;

		$(clonedElm).offset({
        	left: event.pageX + xOffset,
        	top: event.pageY + yOffset
        });

        return false;
	}

	function onMouseUp (event)
	{
		//check if object is dropped on droppable element
		var droppableElements = $(".rk_droppable");
		if (droppableElements.length == 0)
		{
			cancelDrop(event);
		}
		else
		{
			var droppableElm = null;
			for (var i = droppableElements.length-1; i >= 0; i--)
			{
				if (isLocationInElement(droppableElements[i], event.pageX, event.pageY))
				{
					droppableElm = droppableElements[i];
					break;
				}
			}

			if (droppableElm == null)
				cancelDrop(event);
			else
				performDrop (event, droppableElm);
		}

		mouseDown = false;
		clonedElm = null;
		xOffset = 0;
		yOffset = 0;
    }

	function cancelDrop (event)
	{
		if (clonedElm == null)
			return;
		if (!$(clonedElm).hasClass("rk_clonable"))
		{
			$(clonedElm).remove();
		}
		clonedElm = null;
	}

	function performDrop (event, droppableElm)
	{
		//blow up images
		if (event.srcElement == undefined && event.target != undefined)
			event.srcElement = event.target;

		//check element has source attribute
		var src = $(event.srcElement).attr("src");

		if (src != undefined && $(event.srcElement).hasClass("rk_thumbnail"))
		{
			var newImage = "<img src='" + src + "' class='rk_draggable'>";
			var newImageElm = $(newImage).appendTo($(droppableElm));
			//remove thumb nail
			$(clonedElm).remove();
		}
		//$(clonedElm).remove();
		clonedElm = null;
	}

	function isLocationInElement (element, x, y)
	{
		var elmOffset = $(element).offset();
		if (x >= elmOffset.left && x <= (elmOffset.left + $(element).width()) &&
			y >= elmOffset.top && y <= (elmOffset.top + $(element).height()))
			return true;
		return false;
	}
</script>