Some things to check before release:

• Add support for reading TIFFs with PlanarConfiguration=2  #5364 (comment): fuzz crash
• Use LZW encoding when saving GIF images #5291: release notes
• Update config for FriBiDi dynamic linking pillow-wheels#181 is needed for the Raqm/FriBiDi changes
• Fuzzers are good
• https://github.com/python-pillow/pillow-security/pull/9 in the pillow-security repo. Release notes should be basically the commit messages

Main Release

Released quarterly on January 2nd, April 1st, July 1st and October 15th.

• Open a release ticket e.g. Release Pillow 5.2.0 on July 1, 2018 #3154
• Develop and prepare release in master branch.
• Check GitHub Actions and AppVeyor to confirm passing tests in master branch.
• Check that all of the wheel builds Pillow Wheel Builder pass the tests in Travis CI and GitHub Actions.
• In compliance with PEP 440, update version identifier in src/PIL/_version.py
• Update CHANGES.rst.
• Run pre-release check via make release-test in a freshly cloned repo.
• Create branch and tag for release e.g.:

  git branch 5.2.x
  git tag 5.2.0
  git push --all
  git push --tags

• Create and check source distribution:

  make sdist
  twine check dist/*

• Create binary distributions
• Check and upload all binaries and source distributions e.g.:

  twine check dist/*
  twine upload dist/Pillow-5.2.0*

• Publish the release on GitHub
• In compliance with PEP 440, increment and append .dev0 to version identifier in src/PIL/_version.py

Binary Distributions

Windows

• Contact @cgohlke for Windows binaries via release ticket e.g. Release 2.9.0 on July 1, 2015 #1174.
• Download and extract tarball from @cgohlke and copy into dist/

Mac and Linux

• Use the Pillow Wheel Builder:

  git clone https://github.com/python-pillow/pillow-wheels
  cd pillow-wheels
  ./update-pillow-tag.sh [[release tag]]

• Download wheels from the Pillow Wheel Builder release
  and copy into dist/

Publicize Release

• Announce release availability via Twitter e.g. https://twitter.com/PythonPillow/status/1013789184354603010

Documentation

• Make sure the default version for Read the Docs is up-to-date with the release changes

Docker Images

• Update Pillow in the Docker Images repository

  git clone https://github.com/python-pillow/docker-images
  cd docker-images
  ./update-pillow-tag.sh [[release tag]]