This Ruby gem is made for image simularity comparison, using the C libary libpuzzle.

Install

gem install libpuzzle

Make sure you have installed libpuzzle (>= 0.11) first.

Install Libpuzzle

Homebrew:

brew install libpuzzle

APT:

apt-get install libpuzzle1 libpuzzle-dev

Compile:

sudo apt-get install -qq libgd2-xpm-dev
wget http://download.pureftpd.org/pub/pure-ftpd/misc/libpuzzle/releases/libpuzzle-0.11.tar.bz2
tar -xvj -f libpuzzle-0.11.tar.bz2
cd libpuzzle-0.11 && ./configure && make && sudo make install

Since the object file is located in /usr/local/lib, you might want to export LD_LIBRARY_PATH before gem installation, for example:

export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib
gem install libpuzzle

Usage

# load image
p1 = Puzzle.new('foo.png')
p2 = Puzzle.new('bar.png')

p1.similar? p2 # default threshold is 0.6
p1.similar? p2, threshold: 0.7

# get exact distance
p1.distance p2

# compress
p1.compress # => compressed string

# uncompress
Puzzle.uncompress 'COMPRESSED_STRING' # => #<Puzzle>

Integrate with ActiveRecord

Follow the naming convention of ActiveRecord, the database schema will look like:

+---------------------------------+
|            signatures           |
+---------------------------------+
|   id   | signature | picture_id |
+--------+-----------+------------+

+-------------------------------------+
|                words                |
+-------------------------------------+
| id | position | word | signature_id |
+----+----------+------+--------------+

class Word < ActiveRecord::Base
  belongs_to :signature
end

class Signature < ActiveRecord::Base
  K, N = 10, 100
  has_many :words

  def cut_vectors_into_words!
    puzzle = Puzzle.uncompress signature
    i = 0
    while i < N && word = puzzle.vector.byteslice(i, K)
      words.find_or_create_by! word: word, position: i
      i += 1
    end
  end

  def similar_signatures
    Signature.distinct.joins(:words)
      .where('EXISTS (SELECT * FROM words AS _words WHERE _words.sig_id = ? AND _words.position = words.position and _words.word = words.word)', id)
      .where.not(id: id)
      .select{ |sig| Puzzle.uncompress(sig.signature) == Puzzle.uncompress(signature) }
  end

end