title: How do I make an OS X application react when a file, picture, etc is dropped on its dock icon?
body: <p>Some applications, like Photoshop, allow users to drag a picture from a web browser, or drag a file from the filesystem, onto the application's icon in the dock.  Doing this opens the file in that application.</p>
  
  <p>How is this done?  I'd like to use Cocoa and Objective-C, but I'm interested in any solutions in any languages. </p>