Hello,

the first problem is that you are using sh404sef and it must be configured correctly otherwise sitemaps are not ok.
Refer to this FAQ http://storejextensions.org/faq/can-jsitemap-work-with-sh404sef.html
or the PDF document downloadable from the purchased products area.

After that if the images sitemap is still empty the problem could be server related, the crawler for images and videos sitemap could be blocked.

In more details try to open the Links Analyzer and check if links are reported as 200 OK HTTP status code, if not ir means that the crawler is blocked. More info at this FAQ: http://storejextensions.org/faq/my-images-sitemap-doesn-t-embed-all-images-in-my-site-what-could-be-the-problem.html

John