service by a credentials json. creds := credentials.NewApplicationCredentials("credentials.json") config := NewConfig().WithCredentials(creds) client, err := pigeon.New(config) if err != nil { panic(err) } // To call multiple image annotation requests. feature := pigeon.NewFeature(pigeon.LabelDetection) batch, err := pigeon.NewBatchAnnotateImageRequest([]string{"lenna.jpg"}, feature) if err != nil { panic(err) http://kaneshin.github.io/2016/02/27/pigeon/