If the images sitemap is empty it could be not a problem related to the 'media' folder or K2 extension.
A possible issue could be that reported at this forum thread due to server setup:
http://storejextensions.org/forum/view/10-jsitemap/645-re-problem-with-image-xml.html
The first thing to check is if some images not strictly related to K2 are indexed or the image sitemap is always empty.
In the case you can contact me at
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providing site details and access.
Cheers,
John
