Attachment pages not added to the sitemap?

Hi Arne – thank you for a great plugin.

I notice that WordPress attachment pages are not added to the XML sitemap by default. Currently I am adding them to the ‘additional pages’ section of the plugin options but I am not sure if this is necessary/beneficial?

Here is an example of an attachment page:
http://www.cathedralcityguide.co.uk/2014/02/modern-day-censing-angel-at-norwich-cathedral-the-revival-of-a-medieval-tradition/censing-angel-norwich-cathedral/

Please can you advise? Thanks – James

https://wordpress.org/plugins/google-sitemap-generator/