The boot logo is a file called logo.16
It is in the boot.img. To view the boot.img : ( as root )
Code:
cp /cdrom/KNOPPIX/boot.img /tmp/
mkdir /mnt/bootimg
mount -o loop /tmp/boot.img /mnt/bootimg
Now, in /tmp/bootimg you should have :
boot.msg f1 ldlinux.sys logo.16 miniroot.gz syslinux.cfg vmlinuz

these files are for Syslinux and you should read the docs there about the display format ( relating to the f1 file and others )

the logo.16 file is a lss16 format image.
you should have the program ppmtolss16 , which turns a ppm image into a lss16 format image suitable for booting.

The image must be less than 640x480 or less. 640x400 leaves room at the bottom for the boot prompt.

It also must be 16 colors.
use the programs giftopnm or pngtopnm to change your gif or png 16 color image into pnm format, then pnmtolss16, which you can put in /tmp/bootimg.

then you can
Code:
unmount /mnt/bootimg
and then use that boot image when making the ISO file for your CD