Which app did the Drag n Drop start from?

Does anyone know how I might be able to capture which application a Drag-n-Drop action originated in?

I thought it would be in the Source property of the DragInfo object but all I get is a missing value.

I have a table view that I want to receive drops into. The problem I have is that the end user will usually drop files into this table from iView but may drop files from the Finder instead. I need to handle the dropped items differently depending on where they come from.