<?php
class CustomImage extends DataObject {
   //db fields
   static $db = array (
'Description' => 'Varchar(100)'
);

   /**
    * Our custom image class contains one image that is used on one page.
    */
   public static $has_one = array (
      'SliderImage' => 'Image',
      'PageRedirect' => 'SiteTree'
   );

   /**
    * Popup for editing a single image.
    *
    * @return FieldSet The iframe for editing the image.
    */
   public function getCMSFields(){
      return new FieldSet(
         new FileIFrameField('SliderImage')
      );
   }   
}

   public static $has_many = array(
   'CustomImages' => 'CustomImage',
   );

function getCMSFields() {
      $fields = parent::getCMSFields();
      
      //SliderImages
      $images = new ImageDataObjectManager(
   $this,
   'CustomImages',
   'CustomImage',
   'SliderImage'
      );
      
      
      return $fields;
   }
}