Verified
openshift v3.9.30
kubernetes v1.9.1+a0ce1bc657
etcd 3.2.16

Reproduce steps:
1. Edit dc with invalid image reference in 'image' field like below:
        image: docker-registry.default.svc:5000/dyan/cakephp-mysql-example@sha256:latest

2. Prune images
 $ oc adm prune images --keep-tag-revisions=0 --keep-younger-than=0 --token=jf9HRi58RqN0GqBerRyn9UHXHxAvQImhlr6tJ5RhDYE --confirm --loglevel=4

Failed to build graph!

The following objects have invalid references:

  Pod[dyan/cakephp-mysql-example-6-hook-pre]: invalid docker image reference "docker-registry.default.svc:5000/dyan/cakephp-mysql-example@sha256:latest": invalid reference format
  ReplicationController[dyan/cakephp-mysql-example-6]: invalid docker image reference "docker-registry.default.svc:5000/dyan/cakephp-mysql-example@sha256:latest": invalid reference format
  DeploymentConfig[dyan/cakephp-mysql-example]: invalid docker image reference "docker-registry.default.svc:5000/dyan/cakephp-mysql-example@sha256:latest": invalid reference format

Either fix the references or delete the objects to make the pruner proceed.
F0516 03:40:11.697121    1269 helpers.go:119] error: failed to build graph - no changes made

3. Prune images with option '--ignore-invalid-refs'
could prune images without errors

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2018:1796