Sitemap is very important SEO factor to crawl the website by Search Engines.
We can add images to xml sitemap is easy.. Refer the following example,
<?xml version=”1.0″ encoding=”UTF-8″?>
<urlset xmlns=”http://www.sitemaps.org/schemas/sitemap/0.9″
xmlns:image=”http://www.google.com/schemas/sitemap-image/1.1″>
<url>
<loc>http://example.com/sample.html</loc>
<image:image>
<image:loc>http://example.com/image.jpg</image:loc>
</image:image>
</url>
</urlset>
You can follow the Google webmaster instruction for more effectively to add images in sitemaps