Drag and Drop, OS X

I'm trying to build a Mac desktop app that includes functionality to drag and drop images onto an InDesign page, just like the Finder can do. I've been trying to work with the pasteboard types to pass either an NSString or NSURL to the pasteboard and then to InDesign to place the image. But so far, I have had no success. I can make a string of text get placed on the page, but not an image.

Is there something I am missing? Is there some strange ID quirk that relies on some not-well-documented Finder pasteboard function?

I'm passing something like this:

@"file://localhost/Users/chris.paveglio/Desktop/test/Screen%20shot%202012-03-22%20at%2010.25.29%20AM.png"

I tried this old bit of Apple sample code called "Pasteboard Peeker" and that showed me nearly the exact same pasteboard items getting dragged from the Finder as get passed from my app.

Chris