scanner.conf

start on startup
exec /usr/local/bin/scanner.rb

scanner.rb

#!/usr/bin/ruby

require "sane"
require "fileutils"
require "tempfile"

loop do
  scan = nil

  begin
    Sane.open do |sane|
      device = sane.devices.find do |device| 
        device.vendor == "Canon" && device.model == "LiDE 100"
      end
      if device
        device.open do
          while scan.nil?
            if device[:file]
              scan = ["--device", device.name, 
                      "--mode", "Lineart", 
                      "--resolution", "300"]
            end
            sleep(0.5)
          end
        end
      end
    end
  rescue Sane::Error => exception
  end

  if scan
    tempfile = Tempfile.new("scan")
    tempfile.close

    system("scanimage", *scan, :out => tempfile.path)

    output_dir = "/nfs/media/Scans"
    FileUtils.mkdir_p(output_dir, :mode => 0777)

    output_file = "#{output_dir}/#{Time.now.strftime("%Y%m%d%H%M%S")}.png"
    system("convert", tempfile.path, output_file)

    tempfile.unlink
  else
    sleep(60)
  end
end