This is an example set of prototype images (available under https://hub.docker.com/u/healthcheck) for enabling HEALTHCHECK behavior in the official images.
These images are not maintained and are only provided as a reference in implementing your own HEALTHCHECK.
See docker-library/cassandra#76 (comment) for the rationale for why these don't get added to the official images directly.
See github.com/docker-library/oi-janky-groovy/healthcheck-pipeline.groovy for the script which builds and pushes these to the healthcheck namespace on Docker Hub.