The engines regularly update the sitemap format to better take into account the resources of a site. Last November, Google News format was changing, today Google announces an evolution to better take into account images …In a site template, many images are used without that they are relevant for image search engines, thanks to the new format, you will be able to indicate the important images to index for each of your pages thanks to the tag .
Concretely this is what your sitemap should look like:
http://example.com/sample.html
http://example.com/image.jpg
This evolution has two main uses:
- Indicate the important images and ignore the less important ones,
- Indicate images that are not easily accessible via the code but visible on the page, those in javascripts for example.
For more information on this evolution of the sitemap, you can go here.