PHP Google_Service_Visionを使うには？

<?php
namespace App\Console\Commands;
use Illuminate\Console\Command;

class GoogleVisionSample extends Command
{
  protected $signature = 'vision';
  protected $description = '';

  public function handle()
  {
    // サービスアカウントのJSON
    $google_credentials_json =<<< 'GOOGLE_CREDENTIALS_JSON'
{
  "type": "service_account",
  :
  "universe_domain": "googleapis.com"
}
GOOGLE_CREDENTIALS_JSON;

    $client = new \Google_Client();
    $client->setScopes( \Google_Service_Vision::CLOUD_VISION );

    // 認証
    $auth = tempnam(sys_get_temp_dir(),'auth-');
    file_put_contents($auth,$google_credentials_json);
    $client->setAuthConfig($auth);
    unlink($auth);

    // Google_Service_Visionオブジェクトを作成
    $service = new \Google_Service_Vision($client);

    // 画像を読み込む
    $menkyo = file_get_contents('/deploy/laravel/app/Console/Commands/menkyo.jpg');
    $img = new \Google_Service_Vision_Image(['content' => base64_encode($menkyo)]);

    // 画像分析リクエストを送信
    $request = new \Google_Service_Vision_AnnotateImageRequest();
    $request->setImage( $img );
    $request->setFeatures([
      new \Google_Service_Vision_Feature([
        'type' => 'TEXT_DETECTION', // テキスト検出を指定
        'maxResults' => 10          // 最大検出結果数
      ])
    ]);
    $batchRequest = new \Google_Service_Vision_BatchAnnotateImagesRequest();
    $batchRequest->setRequests([$request]);
    $response = $service->images->annotate($batchRequest);
    $text =  $response[0]->fullTextAnnotation->text;
    dd( $text );
  }
}