post on google plus can't post on Google+ with image or video attachment single or multiple

Question

I am posting on google plus account but I can post only post text. How can I post images or videos?

This is my code so far:

$service = new Google_Service_PlusDomains($client);
$activity = new Google_Service_PlusDomains_Activity(
   array(
      'access' => array(
          'items' => array(
              'type' => 'domain'
          ),
          'domainRestricted' => true
      ),
      'verb' => 'post',
      'object' => array(
          'originalContent' => "Post using Google API PHP Client Library! 1" ,
          'attachments' => ['image'=>array('url'=>$img_path)]
      ), 

   )
);

$newActivity = $service->activities->insert($user->id, $activity);    

var_dump($newActivity);