1) Default Structure Data Logo: The logo should be a rectangle, not a square. The logo should fit in a 60x600px rectangle., and either be exactly 60px high (preferred), or exactly 600px wide. For example, 450x45px would not be acceptable, even though it fits in the 600x60px rectangle. More in detail at https://developers.google.com/search/docs/data-types/article#logo-guidelines
2)Default Post Image: It is recommended to add Default Post image, which will be shown as featured image when you don’t add any featured images to post. If you don’t upload the Post image, it may lead to Structure Data Error in Search Console.
Default Post Image width & height:You can also provide Height and Width for Default Post Image, 700×550 is the default value. You can have any values higher than the default value.
3) Thumbnail for VideoObject: If there is video on your page and you wish to set custom Video Thumbnail for that.
4) If you don’t have specific images for page/post, you can set your site logo etc as image
5) Recommended image size for post: medium 300×300 and it fits good on amp pages.
6) Without images, amp returns validation errors. By default it will take image from featured image of a page/post.
