Follow Webmaster Guidelines and best practices for publishing images to increase the likelihood that your images can be found in Image Search results. Additionally, you can use Google image extensions for sitemaps to give Google more information about the images available on your pages. Image sitemap information helps Google discover images that we might not otherwise find (such as images your site reaches with JavaScript code), and allows you to indicate images on your site that you want Google to crawl and index.

You can use a separate sitemap to list images, or you can add image information to an existing sitemap. The following example shows a sitemap entry for the page http://example.com/sample.html, which contains two images.

  
    http://example.com/sample.html
    
      http://example.com/image.jpg
    
    
      http://example.com/photo.jpg
    
   
 

You can list up to 1,000 images for each page, using the syntax outline in the example above!

XML namespace

xmlns="http://www.google.com/schemas/sitemap-image/1.1"

Image tag definitions

Tag	Required	Description
	Yes	Encloses all information about a single image. Each tag can contain up to 1,000 tags.
	Yes	The URL of the image. In some cases, the image URL may not be on the same domain as your main site. This is fine, as long as both domains are verified in Search Console. If, for example, you use a content delivery network such as Google Sites to host your images, make sure that the hosting site is verified in Search Console. In addition, make sure that your robots.txt file doesn’t disallow the crawling of any content you want indexed.
	Optional	The caption of the image.
	Optional	The geographic location of the image. For example, Limerick, Ireland.
	Optional	The title of the image.
	Optional	A URL to the license of the image.

* Nguồn: Google Search Console