Custom Field Generate URL Screenshot

Anh – I found this code snippet and wondered if this could be modified to work with MB? Turns out that there is a third-party ACF addon that does the same thing…

add_shortcode('ss_screenshot', 'ss_screenshot_shortcode');
 function ss_screenshot_shortcode($atts){
  $width = intval($atts['width']);
  $width = (100 <= $width && $width <= 300) ? $width : 200;
  $site = trim($atts['site']);

if ($site != ''){
 $query_url =  'http://s.wordpress.com/mshots/v1/' . urlencode($site) . '?w=' . $width;
  $image_tag = '<img alt="' . $site . '" width="' . $width . '" src="' . $query_url . '" />';
 echo '<a href="' . $site . '">' . $image_tag . '</a>'; 
}else{

echo 'Bad screenshot URL!';
}
}

My guess is I would first have to create a special field type for this to work, so I would appreciate help with that too if this is possible.