A registry uses up to three pieces of information to identify a particular image: Name An image name can range from simple to complex, depending on the registry that stores the image: nginx, servers/nginx, or example.com/servers/nginx. Tag The tag typically refers to the version of the software installed (v1.2.3), though tags are really just arbitrary strings. The tags latest and stable are often used to indicate "the most recent version" and "the most recent production-ready version," respectively. Digest Sometimes it is important to pull a very specific version of an image. Since tags are mutable, there is no guarantee that at any given time a tag refers to exactly a specific version of the software. So registries support fetching images by digest, which is a SHA-256 or SHA-512 digest of the image's layer information.