Docs

The Details

Cover images

As the basic documentation for Cards says, when you choose to have a card with a cover image, that image will be used as the cover of the post corresponding to the card in your site.

This means an <img> tag it will be placed inside the <header> of the <article> tag representing your post, both in lists and labels views, where relevant cards are shown in a list, and in the proper card page.

In all these places the <img> tag will be surrounded by an <a> tag, for making it clickable like the title of the card itself.

My cover isn't showing

Sometimes a theme can make a design decision and deliberately hide cover images. That sometimes is for better, but you have the power to nullify their decision by adding the proper CSS declarations.