I think I found out how to get it working. My first attemp, which worked was to execute the following script after the icon appeared on the screen:

#! /bin/sh
# This is a small script to mount the camera and
# open emacs. When emacs is closed, the camera is
# unmounted.
sleep 1
echo "sleeping 4"
sleep 1
echo "sleeping 3"
sleep 1
echo "sleeping 2"
sleep 1
echo "sleeping 1"
sudo mount -t vfat /dev/sda /media/sda
sleep 1
emacs /media/sda/dcim
sudo umount /dev/sda
echo "camera is unmounted."

Then scouring around in /etc/ I found the file /etc/udev/knoppix.rules and modified it so that it used my user id and group rather than that of knoppix. It now works as I expected it to work.