See commands below (no credentials needed for that image):

$ reg digest registry.access.redhat.com/rhscl/mysql-57-rhel7
invalid checksum digest format

$ docker pull registry.access.redhat.com/rhscl/mysql-57-rhel7
Using default tag: latest
latest: Pulling from rhscl/mysql-57-rhel7
Digest: sha256:6652ef182f61bf1efa25ea101346d6bf72685ac897902a837cf73b200e3a5b2d
Status: Image is up to date for registry.access.redhat.com/rhscl/mysql-57-rhel7:latest

version tested: v0.15.8
environment: MacOS High Sierra 10.13.6