First point your browser to the Aladin Java applet (1) at http://aladin.u-strasbg.fr/AladinJava
Click on "Load..." to bring up the Server Selector window (2).
Click on the "File" tab at the top of that window (3), then browse in your local machine for the image file. If you would like a sample image file, download this FITS image of a galaxy cluster.
Click the "Submit" button (5), and you should now see your image displayed.
Next, click on the right of the Server Selector the "NED" tab (4).
Click "Submit" again (5), and you should see the NED sources overlaid on your image (6). You can get more information about each of these sources by clicking on it.
Aladin can do much more that this simple overlay. Read about Aladin in the "Help...." tab.
