Odyssey Change the screensaver pictures?

When turning off my Odyssey, it displays one of several (apparently) built-in pictures: Jules Verne's portrait, Illiad+Odyssey front cover, Moby Dick sketch, etc. (did not notice if they show at random or in cycle, but it does not matter).

I would like to change the screen saver by putting in my own picture(s). So I connected the device to my PC (Windows 7) and browsed through the Odyssey directories but did not find any image file relating to the screen saver ones.

Is there actually any way to change them?

Thanks in advance for your help (and no big deal if there is none!)