To remove all Docker images that match a certain repo and tag using Bash:
$ docker images --filter "reference=*/sitecore*:9.1.0-20190717" -q --no-trunc | xargs docker rmi
Using Powershell:
PS> docker images --filter "reference=*/sitecore*:9.1.0-20190717" -q --no-trunc | %{docker rmi $_}