How the "Guest User" picture in Ubuntu 12.04 can be changed?
The user picture appear, for example, in the user menu.
This image is seen in every user's menu, so I guess it's just a matter of finding where the silhouetted bust image is, and being able to change it or creating a soft link with its name to the desired substitute picture.
Since the Guest User would never see the picture, I figure that there is nothing I would put in
/etc/guest-session/skel/ (as per How do I change the guest session defaults) or in
/etc/skel/ (a folder mentioned in how to change default launcher icons in unity for a new user?)?