Is there anyway to know if images are overlapping in a droppable area.

Is there anyway to know if images are overlapping in a droppable area.

I am using the JQuery UI draggable and droppable plugins.
I have a droppable area where I drag the draggable images. Is there anyway to detect if two of the droppable images overlap?
If they do overlap is there anyway to reject the drag request?

Thanks.