Automated docker image tagging is available on dockerhub! I fiddled with this recently and wanted to share my findings, jumping on this thread (hope it’s ok!)
So I have a public GitHub repo with an automated build link on dockerhub. I want the :latest tag to be updated every time I push to the master branch. Also, I want :X, :X.Y and :X.Y.Z tags to be created for every release I create on GitHub (tagged as vX.Y.Z on GitHub).
Here is how the build settings config looks like to support this:

And in text so it’s easier to copy-paste:
| Type | Name | Dockerfile Location | Docker Tag Name |
|--------|-----------------------------------|---------------------|-----------------|
| Branch | master "https://stackoverflow.com/" latest |
| Tag | /^v([0-9]+)\.([0-9]+)\.([0-9]+)$/ "https://stackoverflow.com/" {\1} |
| Tag | /^v([0-9]+)\.([0-9]+)\.([0-9]+)$/ "https://stackoverflow.com/" {\1}.{\2} |
| Tag | /^v([0-9]+)\.([0-9]+)\.([0-9]+)$/ "https://stackoverflow.com/" {\1}.{\2}.{\3} |
Hope this helps!