hoge.rb

elsif %r#^http://stat\.ameba\.jp/user_images/.+\.(jpe?g|gif|png)$# =~ m
  require 'open-uri'
  file = Time.now.to_i
  open("./ameba_#{file}.#{$1}", 'wb') do |file|
    open(m, 'Referer' => 'http://ameblo.jp/') do |data|
      file.write(data.read)
    end
  end
  url = `./gyazo ameba_#{file}.#{$1}`.gsub("\n","")
  File.delete("ameba_#{file}.#{$1}")
  "#{url.sub("//","//cache.")}.#{$1}"
end

sample.rb

require 'open-uri'
m = 'http://stat.ameba.jp/user_images/20130623/00/project-imas/e2/74/j/o0639082912585013666.jpg'
open('./hogera2.jpg', 'wb') do |file|
  open(m, 'Referer' => 'http://ameblo.jp/') do |data|
    file.write(data.read)
  end
end