title: Accept drag & drop of image from another browser window
body: <p>In Javascript, I know how to set up a drag &amp; drop target that accepts file uploads from the user's computer. How can I set up a drop target that accepts images that are dragged from another website? All I need to know is the URL of the image that they've dragged.</p>
  
  <p>I know this is possible, since Google Docs accepts image drops from other websites. Any idea how they're doing it?</p>