1

The docker help was consulted:

Usage:  docker [OPTIONS] COMMAND

A self-sufficient runtime for containers

Options:
      --config string      Location of client config files (default "/home/ben/.docker")
  -c, --context string     Name of the context to use to connect to the daemon (overrides DOCKER_HOST env var and default context set with "docker context use")
  -D, --debug              Enable debug mode
  -H, --host list          Daemon socket(s) to connect to
  -l, --log-level string   Set the logging level ("debug"|"info"|"warn"|"error"|"fatal") (default "info")
      --tls                Use TLS; implied by --tlsverify
      --tlscacert string   Trust certs signed only by this CA (default "/home/ben/.docker/ca.pem")
      --tlscert string     Path to TLS certificate file (default "/home/ben/.docker/cert.pem")
      --tlskey string      Path to TLS key file (default "/home/ben/.docker/key.pem")
      --tlsverify          Use TLS and verify the remote
  -v, --version            Print version information and quit

Management Commands:
  builder     Manage builds
  config      Manage Docker configs
  container   Manage containers
  context     Manage contexts
  engine      Manage the docker engine
  image       Manage images
  network     Manage networks
  node        Manage Swarm nodes
  plugin      Manage plugins
  secret      Manage Docker secrets
  service     Manage services
  stack       Manage Docker stacks
  swarm       Manage Swarm
  system      Manage Docker
  trust       Manage trust on Docker images
  volume      Manage volumes

Commands:
  attach      Attach local standard input, output, and error streams to a running container
  build       Build an image from a Dockerfile
  commit      Create a new image from a container's changes
  cp          Copy files/folders between a container and the local filesystem
  create      Create a new container
  diff        Inspect changes to files or directories on a container's filesystem
  events      Get real time events from the server
  exec        Run a command in a running container
  export      Export a container's filesystem as a tar archive
  history     Show the history of an image
  images      List images
  import      Import the contents from a tarball to create a filesystem image
  info        Display system-wide information
  inspect     Return low-level information on Docker objects
  kill        Kill one or more running containers
  load        Load an image from a tar archive or STDIN
  login       Log in to a Docker registry
  logout      Log out from a Docker registry
  logs        Fetch the logs of a container
  pause       Pause all processes within one or more containers
  port        List port mappings or a specific mapping for the container
  ps          List containers
  pull        Pull an image or a repository from a registry
  push        Push an image or a repository to a registry
  rename      Rename a container
  restart     Restart one or more containers
  rm          Remove one or more containers
  rmi         Remove one or more images
  run         Run a command in a new container
  save        Save one or more images to a tar archive (streamed to STDOUT by default)
  search      Search the Docker Hub for images
  start       Start one or more stopped containers
  stats       Display a live stream of container(s) resource usage statistics
  stop        Stop one or more running containers
  tag         Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE
  top         Display the running processes of a container
  unpause     Unpause all processes within one or more containers
  update      Update configuration of one or more containers
  version     Show the Docker version information
  wait        Block until one or more containers stop, then print their exit codes

Run 'docker COMMAND --help' for more information on a command.

The assumption was that there should be a kind of compare command. How could one compare a local image with one in a private registry? For example, if nginx:1.17.5 has been pulled locally and resides in a private docker registry then a command should indicated that:

docker compare nginx:1.17.5 quay.io/some-org/nginx:1.17.5

the command should return:

exit 1, the docker image already resides in the docker private registry
2

A related Q&A was already created on StackOverflow back in the day.

Several answers simply do a docker pull image-to-be-checked. If exit 0, the image exists in a certain registry. If not then the image seems to be omitted. However, if an image is large, e.g. X>1GB or the (office) internet is slow (due to proxies), this could take a while.

The best option to mitigate this is to use docker manifest inspect docker-image as suggested by @morty in conjunction with DOCKER_CLI_EXPERIMENTAL=enabled as suggested in a comment by @ChrisDeacy

Although this command works for dockerhub images, it fails if images have to be checked on quay.io:

unsupported manifest media type and no default available:
application/vnd.docker.distribution.manifest.v1+prettyjws

Therefor I decided to stick to the docker pull approach to make the check docker-registry agnostic.

Today I released version 1.0.0 of Docker Image Patrol (DIP). This tool is able to check whether an image exists in a docker-registry. One could check the existence by running:

./dip -image nginx -registry quay.io/some.org/ -debug
DEBU[0000] debug: true; image: nginx; registry: quay.io/some.org/ 
DEBU[0002] Command: docker pull quay.io/some.org/nginx; Output: Using
default tag: latest
Error response from daemon: unauthorized: access to the requested resource
is not authorized 
DEBU[0002] 1                                            
Is image: 'nginx' absent in registry: 'quay.io/some.org/'? -> true
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