I wrote a plugin for the Bludit CMS to create a better sitemap file, which adds more info and helps avoiding Google error notes.
This plugin is based on the original Sitemap Plugin. It adds the post's image, creates a mobile attribute and puts the change frequency attribute based on the last edited time of the post.
You can download it from here. Disable the Sitemap Plugin before enable this one.
The original plugin's XML output:
BetterSitemap's XML output: