Google Clarifies How It Picks Thumbnails For Search, Discover

Google has publicized and updated its documentation to explain how it selects thumbnail images for Search results and Google Discover.

The company says the changes are meant to remove confusion and make things clearer for publishers.

The update appears on two Search Central pages: Image SEO best practices and the Discover help page. In both places, Google now clearly explains how website owners can suggest which image should appear as a thumbnail.

A New Section on Preferred Images

Google has added a new section called “Specify a preferred image with metadata” to its Image SEO page. The company says this was done based on feedback from users who wanted more clarity about how image previews are chosen.

Google makes it clear that thumbnail selection is automated. Its systems scan different signals on a page before deciding which image to show.

However, publishers are not completely without control. They can guide Google by using specific metadata.

The update confirms that Google looks at both schema markup and the og:image meta tag when picking thumbnails for Search and Discover.

Three Ways to Suggest an Image

Google outlines three methods publishers can use to indicate a preferred image.

First, publishers can use the primaryImageOfPage property within a WebPage structured data block. This tells Google which image represents the page as a whole.

Second, they can attach an image property to the page’s main content entity. This is done using mainEntity or mainEntityOfPage in schema markup, such as within a BlogPosting type.

Third, publishers can use the og:image meta tag. This tag can be placed in the HTML head section of a page. This has long been used for social media sharing previews, and Google has confirmed that it also uses this tag as a signal for thumbnails.

The documentation includes code examples to help publishers implement each method correctly.

Image Quality Still Matters

Beyond technical setup, Google also offers practical advice.

The preferred image should be relevant and clearly connected to the page’s content. Generic images, such as site logos, are not recommended. Images filled with text should also be avoided.

Google advises against very narrow or unusually wide images. Instead, publishers should use high-quality images whenever possible.

For Discover in particular, Google repeats its earlier guidance. Images should be ideally be at least 1,200 pixels wide with high resolution (at least 300KB).

It also follows a 16:9 aspect ratio. Larger images are more likely to perform well in Discover and drive visits.

To qualify for large image previews in Discover, publishers must also enable the max-image-preview:large setting or use AMP. Metadata alone does not make a page eligible.

Why This Update Is Important?

Google says this is not a change in how its systems work. It is simply a clarification.

For publishers, the takeaway is also very straightforward. If you want more control over which an image appears in Search or Discover, you must make sure your structured data and og:image tag clearly point to a strong, high-quality image that represents your content.

If you are already using these methods, this update confirms that they matter. If you are not, Google’s documentation now provides clear guidance on how to get started.

The process has not changed. But the instructions are now much easier to understand.