For the start and shutdown, I like
Code:
convert -crop 117x117+0+1 /usr/share/icons/crystalsvg/128x128/apps/clock.png ppm:- | ppmtofb --stdin --center -w 777 &
For the "safe to turn off now"
Code:
convert /usr/share/icons/default.kde/32x32/actions/exit.png ppm:- | ppmtofb --stdin --center &
Note that in this solution, *zero* additional tools or graphics from the outside are used. (This should make KK happy.) It is all done with what is on the CD. To have a nice animation, I think we would need a small outside app, but there might be possibilities to do it without, too (e. g. a sequence of ppm images played one after the other, I am investigating this).

Now, how should it be implemented? I would prefer a folder "splash" in the /KNOPPIX folder on the CD, where the actual scripts and graphics could be easily modified without touching the initrd. The Knoppix startup and shutdown scripts would just call "/cdrom/KNOPPIX/splash/splash.sh start" and "/cdrom/KNOPPIX/splash/splash.sh stop" for starting and stopping the spash screen, and "/cdrom/KNOPPIX/splash/safeoff.sh start" for showing the shutoff screen.

We can even make them display the splash only if "splash=1" is given at the boot prompt (this should make KK even more happy).