Google uses both schema.org markup and og:image meta tag for thumbnails in Google Search and Discover

Google clarified this within its Google image best practices and Google Discover documentation.

Google Clarifies How It Picks Thumbnails For Search, Discover

Google updated its Image SEO and Discover documentation to explain how schema markup and the og:image meta tag influence ...
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Why Meta Tags Are Still Relevant to SEO - and the Best Way to Use Them

Within the constantly shifting guidelines for what does and doesn’t boost a website’s SEO, meta tags typically don't garner much attention. They don't directly impact Google SEO rankings, but they can ...

Google Explains Why Its Crawler Ignores Your Resource Hints

Google's Gary Illyes clarifies why resource hints do not influence Googlebot's crawling behavior, and notes that HTML ...

How Google Search & Google Discover Picks Image Thumbnails

Google updated its image SEO best practices and Google Discover documentation to clarify how Google picks a preferred image ...