The guidelines for Nginx in the documentation include the single image page url rewrite.
This is used for passing a single image slug to backlight, e.g. as for the url’s used in RSS feeds which include -single at the end of the image slug.
Single Image pages
rewrite ^(.)/(.)-single.php $1/single.php?id=$2&mod_rewrite=on last;
However, the above is incorrect and will not work. Change it to the below for correct redirection.
Single Image pages
rewrite ^(.)/(.)-single $1/single.php?id=$2&mod_rewrite=on last;