How can I tell the robot which images to index?

Use an XML Sitemap file to inform the Yandex robot about the images that need to be indexed on your website. This method allows robots to find not easily accessible content (for example, content that loads using JavaScript).

To do this, add a special entry to the Sitemap file. Here's a sample Sitemap file for a page and an 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	Required	Description
image:image	Yes	Contains information about a single image. Each loc tag can include up to 1000 image:image tags.
image:loc	Yes	Image URL. If the image URL domain differs from your site domain, check that you have confirmed your rights to manage both sites in Yandex.Webmaster. Please also note that the robots.txt file must not ban the indexing of the specified image.
image:caption	No	Image caption. The maximum size is 256 B.
image:geo_location	No	Image shooting location. The maximum size is 256 B.
image:title	No	Image title. The maximum size is 256 B.
image:license	No	Image license URL. The maximum size is 256 B.

Tag	Required	Description
image:image	Yes	Contains information about a single image. Each loc tag can include up to 1000 image:image tags.
image:loc	Yes	Image URL. If the image URL domain differs from your site domain, check that you have confirmed your rights to manage both sites in Yandex.Webmaster. Please also note that the robots.txt file must not ban the indexing of the specified image.
image:caption	No	Image caption. The maximum size is 256 B.
image:geo_location	No	Image shooting location. The maximum size is 256 B.
image:title	No	Image title. The maximum size is 256 B.
image:license	No	Image license URL. The maximum size is 256 B.