nginx force download

nginx.conf

# attachment directory

        location /attachment/  {
            alias /tmp/attachment/;
            types        { }
            default_type application/octet-stream;

            if ($request_filename ~ "^.*/(.+\.png|jpg|gif)$"){
                set $fname $1;
                add_header Content-Disposition 'attachment; filename="$fname"';
            }
        }