identify featured image from attachment array

Maybe somebody has solved this. After retrieving posts, how do you tell which of the attached images is the featured image?
The featured image just shows up like a regular attachment, something like this:

"attachments"=>
[{"id"=>114,
  "url"=>"http://test.com/wp-content/uploads/2015/04/media-6bgImage.jpg",
  "slug"=>"media-6bgimage",
  "title"=>"media-6bgImage",
  "description"=>"",
  "caption"=>"",
  "parent"=>59,
  "mime_type"=>"image/jpeg",
  "images"=> {
    "full"=>{"url"=>"http://test.com/wp-content/uploads/2015/04/media-6bgImage.jpg", "width"=>1600, "height"=>1000},
    "thumbnail"=>{"url"=>"http://test.com/wp-content/uploads/2015/04/media-6bgImage-150x150.jpg", "width"=>150, "height"=>150},
    "medium"=>{"url"=>"http://test.com/wp-content/uploads/2015/04/media-6bgImage-300x188.jpg", "width"=>300, "height"=>188},
    "post-thumbnail"=>{"url"=>"http://test.com/wp-content/uploads/2015/04/media-6bgImage-825x510.jpg", "width"=>825, "height"=>510}
    }
  }
]

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