#!/bin/bash
if [[ $# -lt 2 ]] ; then echo Usage: $0 folder base; exit 1; fi
cd img/$1
for f in *.jpg
do
   mv "$f" "`identify -format %[Exif:DateTimeOriginal] $f`".jpg
done
ls *.jpg | cat -n | while read n f; do mv "$f" "$(($n + $2))".jpg; done