"public domain" software licensing and copyright?

[mmiller3@iupui.edu (Michael A. Miller)]

I'd like to package ImageJ: http://rsb.info.nih.gov/ij/

     "ImageJ is a public domain Java image processing program
     inspired by NIH Image for the Macintosh. It runs, either as an
     online applet or as a downloadable application, on any
     computer with a Java 1.1 or later virtual machine."

There is a copyright and licensing issue that I think needs to be
explored - the author tells me that

    "ImageJ is in the public domain. No license is required.
    There is no copyright. You are free to package the ImageJ
    source code and JAR file with Debian Linux, but please
    include a README file that points to the ImageJ Web page so
    people can get documentation and updates."

I have asked the author to license the work according to one of
the GPL, BSD or Artistic licenses.  Can anyone advise me as to
the need for that?  Are there examples of "public domain"
software in Debian where the issues of copyright and license are
made explicit?

Mike

-- 
Michael A. Miller                      mmiller@debian.org
  Krannert Institute of Cardiology, IU School of Medicine
  Indiana Center for Vascular Biology and Medicine