copy/copy.go
func layerDigestsDiffer(a, b []types.BlobInfo) bool {
	if len(a) != len(b) {
		return true
	}
	for i := range a {
		if a[i].Digest != b[i].Digest {
			return true
		}
	}
	return false
}
func layerDigestsDiffer(a, b []types.BlobInfo) bool {
	if len(a) != len(b) {
		return true
	}
	for i := range a {
		if a[i].Digest != b[i].Digest {
			return true
		}
	}
	return false
}
// layerDigestsDiffer return true iff the digests in a and b differ (ignoring sizes and possible other fields)