title: Determine the source application of current pasteboard content
body: <p>Several OSX clipboard managers from AppStore show the ability to determine the source-application of content that was copied to the clipboard.</p>
  
  <p>I am writing some simple clipboard observer and would like to show the source-application icon near the content, stored in general NSPasteboard. And I would like to know how this can be achieved.</p>
  
  <p>As far as I can see, NSPasteboard doesn't provide any additional info except types of data and data itself.</p>
  
  <p>Maybe there are some events or notifications to know that a 'copy' command was triggered? Or some other ways?</p>