Hi there,
Thanks for this module, however there's still room for improvement, I've got a few suggestions for that matter.
First of all I'd suggest to allow the administrator to choose the sitemap location as /sites/redeseo.es/files/google_image_sitemap/sitemap_xxxx.xml is not a good place to be. Or at least place it on the site root eg. mysite.com/imagesitmap.xml
For what I know it's a good SEO practice to Disallow: /sites/ folder from the robots.txt ... therefore placing the sitemap there by default isn't a good idea.
Second, I'd suggest you allow the administrators to choose the filename too.
Third, find a way no to ask for the Starting Node ID and Ending Node ID, that makes the administrator having to modify image sitemap settings every single time a node with a image is added ... very troublesome, no efficient at all.
That said, thank you very much for your efforts this is a much needed module.
Manuel