xscreensaver "logo" path

[Mihamina Rakotomandimby]

Hi all,

Using Xubuntu Natty, when I lock the screen (or suspend) and then coming 
back,
There is the XscreenSaver login/pass prompt.

I would like to modify the "logo" in the left side, the "fire in front 
of a screen"

When trying on my system, I did not find the path of the file I must edit:
- trying the images files from http://is.gd/NEMgWA failed
- "locate xscreensaver" and trying every result seeming to be an image 
(xpm, png,..) failed.

Would you know what file to overwrite on a debian based system in order 
to have another logo?

Thank you.

-- 
RMA.