pdq-ruby is a Ruby gem that provides a convenient wrapper around the PDQ (Photo DNA Quick) hash algorithm implementation. PDQ is a perceptual image hashing algorithm developed by Facebook (now Meta) that generates compact binary fingerprints of images. These fingerprints can be used to:

• Detect duplicate or near-duplicate images
• Identify similar images even after modifications
• Perform efficient image similarity searches
• Support content moderation and copyright protection

The gem provides a Ruby-friendly interface to the Rust-based PDQ implementation, making it easy to:

• Generate PDQ hashes from images
• Compare images for similarity
• Handle various image formats
• Process images efficiently with native performance

This gem is a wrapper of darwinium-com's pdqhash Rust implementation.

Add this line to your application's Gemfile:

gem 'pdq', git: 'https://github.com/fetlife/pdq-ruby.git'

And then execute:

bundle install

Or install it yourself as:

gem install pdq --source https://github.com/fetlife/pdq-ruby.git

The gem provides a simple interface to generate PDQ hashes from images:

require 'pdq'

# Generate a PDQ hash from an image file
hash, quality = Pdq.pdq_hash("path/to/image.jpg")

# The hash is returned as a hexadecimal string
puts "PDQ Hash: #{hash}"
# => PDQ Hash: 31ab07638e54b8fc49bb6633b1449dc44ebb63f3934d9c5c6cb2678f935dc000

# The quality score indicates the quality of hash (0 - 1.0)
puts "Quality: #{quality}"
# => Quality: 1.0

The pdq_hash method returns an array containing two elements:

1. The PDQ hash as a hexadecimal string (256 bits, represented as 64 hexadecimal characters)
2. A quality score between 0.0 and 1.0 indicating the reliability of the hash
   • 1.0 indicates a high-quality hash
   • Lower scores suggest potential issues with the image or hash generation

Supports any format handled by image::ImageReader.

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install.

To release a new version:

1. Update the version number in version.rb
2. Run bundle exec rake release

This will:

• Create a git tag for the version
• Push git commits and the created tag
• Push the .gem file to rubygems.org

Bug reports and pull requests are welcome on GitHub at https://github.com/fetlife/pdq-ruby. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

The gem is available as open source under the terms of the MIT License.

Everyone interacting in the pdq-ruby project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.