How do I detect if a drag operation was cancelled using NSDraggingInfo or similar?

Question

I've created a subclass of NSImageView and implemented the informal protocol for dragging images between other instances of the same class. I am keeping a reference to the image of the view prior to the dragging operation and am able to set it back to said image given certain criteria.

However, I can't seem to detect if the dragging operation was cancelled. I know that the draggingEnded method is called but it is also called when a drag was successful. Any ideas?