origami-test.rb

#!/usr/bin/ruby
require 'origami'
include Origami

pdf = PDF.read(ARGV.first) 
pdf.pages.each do |page| 
  xobjs = page.Resources[:XObject] 
  xname = xobjs.keys.first 
  obj = xobjs[xname].solve 
  open("new-image.jpg", "r") do |i| 
    obj.Length = i.stat.size 
    obj.data = i.read 
  end 
  obj.Width = 12345 # new-image.jpg¤ÎÉý 
  obj.Height = 54321 # new-image.jpg¤Î¹â¤µ 
  break 
end 

pdf.saveas("new.pdf")

cool