#!/bin/bash

#run this at startup
# set the path to the picture folder
PICDIR=/media/BackingStore/Pictures/JordanAndEgypt
PICNAMES=( $(find $PICDIR | grep -i JPG) )
NUMBER=$RANDOM
MAXFILES=${#PICNAMES[@]}
PIC=${PICNAMES[ $(( NUMBER %=  MAXFILES ))]}

gconftool-2 --type string --set /desktop/gnome/background/picture_filename $PIC