using gnome-open with mailcap data

[Eric Abrahamsen <eric@ericabrahamsen.net>]

So far as I understand it, the best way to get gnus to open images
externally using a different viewer is a ~/.mailcap file with something
like this in it:

image/jpeg; /usr/bin/eog %s

(eog is the default Ubuntu image viewer)

I have two questions about this (apart from the obvious, "is this the
right thing to do"):

1. Why don't wildcards word in the mimetype? Neither image/* nor
   image/.* works, gnus goes back to the default of "display". I need to
   specify image/jpeg.
2. Can I use gnome-open for this sort of thing? It's basically its own
   little mime parser, and knows all the system defaults, and if I'm
   going to pass a file to something outside of gnus/emacs, gnome-open
   knows best what to do with it. Setting gnome-open in my .mailcap file
   just gives me "Displaying /usr/bin/gnome-open
   /tmp/emm.5971frN/IMG_3368.JPG...done" in the minibuffer, and then
   nothing happens.

Any hints welcome!

Thanks,
Eric