How do I tell the robot which images to index?

Use the Sitemap file in XML format to inform Yandex robots about graphic materials to be indexed on your site. This allows robots to find hard-to-access content (for example, content that loads using JavaScript).

To do this, you need to add a special entry to the Sitemap file. See the example Sitemap for one page and one image:

<?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/primer.html</loc>
    <image:image>
      <image:loc>http://example.com/image.png</image:loc>
      <image:geo_location>Karelia</image:geo_location>
    </image:image>
  </url> 
</urlset>

Tag description

Tag	Mandatory	Description
image:image	Yes	Contains information about an image. Each loc tag can include up to 1000 image:image tags.
image:loc	Yes	Image URL. If the domain of the image URL differs from the domain of your site, check that your rights to manage both sites are confirmed in Yandex Webmaster. Note that the robots.txt file mustn't prohibit indexing of the image.
image:caption	No	Image caption. The maximum size is 384 bytes.
image:geo_location	No	Shooting location. The maximum size is 256 bytes.
image:title	No	Image name. The maximum size is 384 bytes.
image:license	No	Image license URL. The maximum size is 256 bytes.

Tag	Mandatory	Description
image:image	Yes	Contains information about an image. Each loc tag can include up to 1000 image:image tags.
image:loc	Yes	Image URL. If the domain of the image URL differs from the domain of your site, check that your rights to manage both sites are confirmed in Yandex Webmaster. Note that the robots.txt file mustn't prohibit indexing of the image.
image:caption	No	Image caption. The maximum size is 384 bytes.
image:geo_location	No	Shooting location. The maximum size is 256 bytes.
image:title	No	Image name. The maximum size is 384 bytes.
image:license	No	Image license URL. The maximum size is 256 bytes.