The repo and the Docker image aren't maintained any more. You can use the code to build your own image, but do not rely on the published one.
A Docker image for Paperkey — an OpenPGP key archiver
Paperkey by David Shaw is a tool that lets you backup OpenPGP keys by printing them on paper. It compresses the key by removing all the unnecessary information and formats it in a way that allows easier re-entering in case a recover is needed.
# pull the image
docker pull nickkaramoff/paperkey
# run the container with volume binding to the current directory
docker run --rm -v $(pwd):/ nickkaramoff/paperkey --secret-key my-secret-key.gpg --output to-print.txt
This is free and unencumbered software released into the public domain.
Paperkey released under the Terms of GNU GPL v2.0.