Image Sitemaps
Google uses XML schemas to define the elements and attributes that can appear in your Sitemap file. A Sitemap may contain both core Sitemap elements and elements specific to Images. You can download the schemas from the links below:
For elements specific to Images:
https://www.google.com/schemas/sitemap-image/1.1/sitemap-image.xsd
For core Sitemap elements:
https://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd