Don't worry! It's only stuff...

#!/bin/bash
 
# add to /etc/sudoers
# USER_NAME ALL=NOPASSWD:/bin/umount /media/USER_NAME/usbdisk-sdb1
 
DEVICE=usbdisk-sdb1
 
# clean
rm /media/${USER}/${DEVICE}/dcim/100nikon/*.jpg
sync
 
# umount
sudo /bin/umount /media/${USER}/${DEVICE}