static $has_many = array (
'Images' => 'ServicePagePhoto'
);

public function getCMSFields()
{
$f = parent::getCMSFields();
$manager = new ImageDataObjectManager(
$this, // Controller
'Images', // Source name
'ServicePagePhoto', // Source class
'Attachment', // File name on DataObject
array(
'Title' => 'Title',
'Description' => 'Description',
'Group' =>'Group',
), // Headings
'getCMSFields_forPopup' // Detail fields
// Filter clause
// Sort clause
// Join clause
);
$f->addFieldToTab("Root.Content.Photo",$manager);
return $f;
}

<div id="slider" class="mb-slider">
<% control Images %>
<div>
<a class="lightbox" title="$Title" rel="$Group" href="$Attachment.URL">
$Attachment
</a>
<br />
<h3>{$Title}</h3>
<br />
<p>$Description</p>
<!----a image2, image3, image 4-->
</div>
<% end_control %>
</div>

<div>
<a href="images/service/door-1.jpg" rel="group1" title="" class="lightbox"> //---This loads first when the lightbox is open up
<img src="images/service/door-big-1.jpg" /> //--- photo displaying (area)
</a>
<a href="images/service/door-2.jpg" class="lightbox" rel="group1" title=""></a> //---This loads second when the lightbox is open up
<br>
<h3>Door Repaint and Stained<br>
<p>Work was performed in a heritage house located in North Adelaide.</p>
</div> //---Group 1

<div>
<a href="images/service/door-3.jpg" rel="group2" title="" class="lightbox">
<img src="images/service/door-big-2.jpg" />
</a>
<a href="images/service/door-4.jpg" class="lightbox" rel="group2" title=""></a>
<br>
<h3>Door Repair and Repaint</h3>
<p>Main Entry door repainted - Mile End.</p>
</div> //---Group 2