registry marks in gnus 5.13

[emacsnews]

I am using gnus 5.13 with emacs 23.0.60.1 in Ubuntu Intrepid
I see no registry marks in my summary buffer.
I have the following lines in my .gnus.el file:

;; gnus registry 
(setq gnus-registry-cache-file "~/.emacs.d/.gnus.registry.eld"
      gnus-registry-max-entries 25000
      gnus-registry-use-long-group-names t
      gnus-registry-install t)
(gnus-registry-initialize)

I have not changed the value of gnus-registry-marks which is:

((Important :char 105 :image "summary_important")
 (Work :char 119 :image "summary_work")
 (Personal :char 112 :image "summary_personal")
 (To-Do :char 116 :image "summary_todo")
 (Later :char 108 :image "summary_later"))

I tried all the default registry marks, and checked with the
gnus-registry-get-article-marks function that the marks have indeed been
allocated.

I suspect it has something to do with the :image property, but this is
not documented in the info files.
Can anyone help me?

aleblanc