/**
  * @param string|array $imageIds
  *
  * @return Image[]
  * @throw HttpException
  */
 protected function validateImages($imageIds)
 {
     if (!is_array($imageIds)) {
         $imageIds = explode(',', $imageIds);
     }
     $images = [];
     foreach ($imageIds as $imageId) {
         /** @var Image $image */
         $image = Image::find($imageId);
         if (!$image) {
             throw new HttpException(404, "Image ({$imageId}) not found.");
         }
         if ($image->userId !== $this->user->id) {
             throw new HttpException(403, "User does not own image ({$imageId}).");
         }
         $images[] = $image;
     }
     return $images;
 }