kyverno/samples/best_practices/restrict_image_registries.yaml

apiVersion : kyverno.io/v1alpha1
kind: ClusterPolicy
metadata:
  name: restrict-image-registries
  annotations:
    policies.kyverno.io/category: Image
    policies.kyverno.io/description: Images from unknown registries may not be scanned and secured. 
      Requiring use of known registries helps reduce threat exposure.
spec:
  rules:
  - name: validate-registries
    match:
      resources:
        kinds:
        - Pod
    validate:
      message: "Unknown image registry"
      pattern:
        spec:
          containers:
          - image: "k8s.gcr.io/* | gcr.io/*"