Tobias Nyholm

Prevents an user to publish a post without a thumbnail. If a user presses the publish button without a thumbnail, the post will 
be saved as a draft. For more information see installation page or the 
<a href="http://www.webfish.se/wp/plugins/require-thumbnail" title="Webfish - WordPress plugin" rel="nofollow ugc">Webfish</a> homepage.

Require Thumbnail

Prevents an user to publish a post without a thumbnail.

Johan Jonk Stenström

Lists categories, author pages and archives with thumbnails. Use shortcode [categorythumbnaillist 1] where 1 is the category id.
Don’t forget to add Featured images to your posts.

Category Thumbnail List

Lists categories, author pages and archives with thumbnails. Use shortcode [categorythumbnaillist 1] where 1 is the category id.

Require Thumbnail vs Category Thumbnail List