It seems as if WC uses it's own built in Lightbox plugin called Pretty Photo which is where the images that are detailed as 'unused' by DNUI are called from. This is because my site uses Woocommerce and a theme which both use images within other places rather than just posts or pages such as headers, footers and galleries. I have tried to use plugins to achieve this end such as DNUI and Cleanup Images but these plugins are either unworkable or in DNUI's case (which has been updated recently and works) do not achieve the exact results that I am after. I am trying to clean out my uploads folders as they are now starting to take up too much room on my server.