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 ...
Search Engine Roundtable

Google Updated Image SEO Best Practices For Embedded Images

Google has made a small update to its image SEO best practices documentation, specific to the "Use HTML image elements to embed images" section. The update seems relatively minor but the changes to ...