How to add a link in Jquery PrettyPhoto to download the image

Question

I am using Jquery PrettyPhoto to have a slide show, however it does not let the users to download the images. Anyone know how can I add a link to it so users will be able to download the images?

Here is my code: (I am using prettyPhoto Widget in Yii, but any answer in general for prettyPhoto will be great)

<?php 
  $this->beginWidget('ext.prettyPhoto.PrettyPhoto', array(
        'id'=>'pretty_photo',
        // prettyPhoto options
        'options'=>array(
            'opacity'=>0.60,
            'modal'=>true,
        ),
    ));
?>
<div class="column4-front image-gallery">

         <a href="/files/show/<?php echo $data->image; ?>" rel="prettyPhoto[pp_gal]" title="<?php echo $data->caption; ?>">
             <img src="/files/show/thumb/<?php echo $data->image; ?>" />
         </a>

</div>
<?php $this->endWidget('widgets.prettyPhoto');?>