An additional note on the "anamorphic flag" (my bad for not being more complete). It is a flag set in your encoding software AND/OR your DVD authoring software. For example, in the freeware "DVDStyler" (a very well implemented GUI to "dvdauthor" -- both at "SourceForge"), the default video descriptor is "auto", where it uses the video's flag for anamorphic display. If you can't encode it with that flag set (or thereafter set the flag with a third party program), you may instruct your authoring software to force it to "16:9" in the parent menu properties and/or the video properties for anamorphic display.

http://www.dvdstyler.org/

Regarding anamorphoric sizes, I'm not sure if the standards of anamorphic lenses are equivalent to DVD standards. So I took your raw frame capture:

and superimposed on an anamorphic capture of the SW DVD and discovered I had to reduce the proportions and size of your capture to fit onto the official release:

This indicates that you must do some resizing, anyway, to get it ready for proper DVD anamorphic size. It shows how much of the picture was cropped for this printing. It also shows what your black border might look like when you're finished. Once displayed from DVD to TV, it will stretch wider for proper display (either 16:9 widescreen or letterboxed in 4:3).