Getting data- value from sender in Polymer

I'm trying to create a lightbox component in Polymer, with it's child items being multiple <img> tags. These will have an src, which is a thumbnail and a data-fullimage attribute, which will contain the path to the full size image.

In the Polymer component, I've set the on-click tag on the image content selector, and any Javascript calls using sender.xyz return the content tag, not the image tag, thus not allowing me to retrieve the path to the full image. Is there any way to get the data-fullimage of the image that is clicked, or even the src value if need be?

Polymer Component

imageClick: function(event, detail, sender) 
{
      console.log(sender);
}

Implementation

<paper-lightbox>
    <img src="img/one.png" data-fullimage="img/one-large.png"></img>
    <img src="img/two.png" data-fullimage="img/two-large.png"></img>
</paper-lightbox>