You can right-click and copy the link,
like so, but it is a problem for NWR in that you can't link to a page that displays the image along with ads and links to NWR sections. The image viewer essentially makes "leeching" the only option. It'd be neat if there were a way to get a link to the image from the image viewer such that if I passed it along to someone, they'd arrive at the image index page and the viewer would automatically load the correct image.