How to change wordpress img attributes - php

Question

Am using Unveil plugin to lazy load images in wordpress. I would like to change the img attributes to something like this.
<img data-src="http://lorempixel.com/g/800/500/city/10" data-src-retina="http://lorempixel.com/g/1280/800/city/10" src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" />
With this link I was able to achieve src now I kindly request someone to help on how to generate data-src and data-src-retina attributes.
Later I want to use them in my function in funtions.php
Bellow is my code snippet, but its not working only the src
function image_tag($html, $id, $alt, $title) {
//generate data url
$type = pathinfo($img, PATHINFO_EXTENSION);
$data = file_get_contents($img);
$src = 'data:image/' . $type . ';base64,' . base64_encode($data);
return preg_replace(array(
'/'.str_replace('//','//',get_bloginfo('url')).'/i',
'/s+width="d+"/i',
'/s+height="d+"/i',
'/alt=""/i'
),
array(
'data-src=" "',
'src="'.$src.'"',
'data-src-retina=" "',
'alt="' . $title . '"'
),
$html);
}
add_filter('get_image_tag', 'image_tag', 0, 4);