Compare a bunch of images to find duplicates

gistfile1.rb

files = Dir.glob("*.png")
compares = {}
files.each do |file|
  files.each do |compare_to|
    key = [file, compare_to].sort.join("-")
    unless compares[key] || file == compare_to
      compares[key] = `compare -metric MAE #{file} #{compare_to} null: 2>&1` 
      puts "#{file} vs #{compare_to} = " + compares[key] # if a comparison yields `0 (0)`, they're the same
    end
  end
end