Google just clarified thumbnail image signals - 3 quiet tweaks SEOs must act on

Google has updated its Search Central documentation to clarify how it selects thumbnail images for Search and Discover results, adding guidance on how site owners can signal a preferred image using structured data and Open Graph metadata.

Key Details

Google added a new "Specify a preferred image with metadata" section to its Image SEO best practices in the Google Images documentation on the developer site.

The new section explains that thumbnail selection is automated and can draw from multiple images on a page, but publishers can indicate a preferred image using structured data properties or the og:image meta tag.

• Use the schema.org primaryImageOfPage property on a WebPage structured data type.
• Attach an image property to the page's main entity via mainEntity or mainEntityOfPage.
• Specify a preferred image in the page head with the og:image meta tag.

The documentation includes code samples for each of these approaches, using JSON-LD markup and standard HTML meta tags.

On its Search Central documentation updates page, Google said the documentation changes were made:

"based on feedback"

The note also confirms that Google uses both schema markup and og:image metadata when selecting thumbnails in Search and Discover.

Google also updated its Discover documentation to reference these image metadata options. The Discover page now recommends using schema.org markup or an og:image tag to indicate a large image for thumbnails and links directly to the new image metadata guidance in the Google Images documentation.

The Discover documentation reiterates that large image previews in Discover require either the max-image-preview:large setting or the use of AMP pages. Image-related schema and og:image metadata can influence which image is chosen as a thumbnail but do not, on their own, make content eligible for large previews.

Across both documentation pages, Google advises against specifying generic images such as logos or images with prominent text. Instead, it recommends high resolution images with appropriate aspect ratios, avoiding images that are extremely narrow or extremely wide.

Background Context

Google's documentation emphasizes that thumbnail images in Search and Discover are selected automatically from multiple image sources on a page. The new guidance clarifies which metadata signals - structured data and Open Graph tags - can inform that selection.

The image-related changes build on a broader revision of Google's Discover documentation that accompanied a February Discover core update. That earlier revision updated recommendations related to clickbait, page experience, and image quality in Discover. The latest additions extend the image section from that update by detailing how publishers can express thumbnail preferences within schema.org markup and Open Graph metadata.

Source Citations

This article is based on publicly available documentation from Google's official developer resources:

• Image SEO best practices - "Specify a preferred image with metadata" section in Google Images documentation.
• Discover documentation - "Images in Discover" guidance on image requirements and metadata.
• documentation updates page - Google Search Central change log noting the update was made "based on feedback."