A pod in OpenShift does not go ready with status: ImagePullBackOff

Issue

• While deploying a pod, it does not go up and it stays in status ImagePullBackOff, pod events shows:

  Normal   Pulling  1h (x2253 over 8d)    kubelet, hostname.com pulling image "docker-registry.default.svc:5000/namespace/app@sha256:..."
  Warning  Failed   20m (x49991 over 8d)  kubelet, hostname.com  Error: ImagePullBackOff
  Normal   BackOff  7s (x50077 over 8d)   kubelet, hostname.com  Back-off pulling image "docker-registry.default.svc:5000/namespace/app@sha256:..."
  

• Can not build an application using a BuildConfiguration with error: Output image could not be resolved.