Script for changing photo creation timestamp (in EXIF metadata and filesystem) in all jpeg's in current directory.

photo-touch.rb

#!/usr/bin/ruby
# encoding: utf-8
#
# Script for changing photo creation timestamp (in EXIF metadata and filesystem)
# If you're using rvm, please run script as `ruby photo-touch.rb`
# Tested in ruby-1.9.3-p125 and ree-1.8.7-2012.02
#
# Install ExifTool: http://www.sno.phy.queensu.ca/~phil/exiftool/install.html
#
# You need next gems for script to work (use gem install gem_name)
#  * active_support (~> 3.0)
#  * mini_exiftool  (note: you need the ExifTool library!)
#
# 2012, Novikov «Envek» Andrey. Use it freely under the MIT license.
#

require 'rubygems'
require 'active_support/all' # A lot of useful stuff here (e.g. 2.weeks.ago)
require 'find'               # For Find.find (walk a directory)
require 'fileutils'          # For FileUtils.touch (change file timestamps)
require 'mini_exiftool'      # Exif metadata editing

# http://stackoverflow.com/questions/4894198/how-to-generate-a-random-date-in-ruby
def time_rand(from = 0.0, to = Time.now)
  Time.at(from + rand * (to.to_f - from.to_f))
end

### CONFIG SECTION ###
offset = 1.day + 4.hours - 20.minutes                             # Shift all timestamps back by offset
#new_time = time_rand((1.day+12.hours).ago, (1.day+6.hours).ago)  # Set a random timestamp in range
#date = (1.day+8.hours+10.minutes).ago                            # To a some defined datetime
#offset = (1.hours / Find.find('./').count).seconds               # For giving all photos sequentally growing timestamps

# Find all jpegs in currrent directory, change timestamps to required
Find.find('./') do |f|
   if f.match(/\.jpg|jpeg|jfif\Z/i)
    photo = MiniExiftool.new(f)
    date = photo.date_time_original - offset  # Calculate it here as you wish
    puts "#{f}\t- #{date}"                    # For debug purposes
    photo.date_time_original = date           # Change EXIF photo creation timestamp
    photo.save
    FileUtils.touch f, :mtime => date         # Change filesystem creation timestamp
   end
end