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.

roganty

Set a default thumbnail using either an image from your image gallery or use your gravatar for posts with no thumbnail set.
This plugin requires your theme to have support for post thumbnails enabled. 
Although no extra code needs to be added to your theme, some alterations might be required for trouble free usage.

Default Post Thumbnail Image

Set a default thumbnail using an image from your gallery or use your gravatar for posts with no thumbnail set

Require Thumbnail vs Default Post Thumbnail Image