As Docker’s Justin Cormack pointed out, you can get hold of a specific version of a container image if you know its hash.
If the tags for a particular version are deleted you can no longer pull the same image by tag. And if a tag is reused for a different version of the image, you’ll get that different version if you pull by tag. The good thing about pull by hash is that you know that you’ll be getting exactly the same thing each time, and you should be able to do that indefinitely (even if you can no longer see the tag for that image on Docker Hub).
