Vincent Dubroeucq

Visit your blog posts listing page, or a single post page, and open up the WordPress customizer.
Under Tiny Thumbnail Settings, choose or upload your default image. That’s it !
Enjoy !

Tiny Default Thumbnail

Allows you to add a default featured image to posts. Just add a default image in your customizer settings !

wphigh

Admin Featured Thumbnail WordPress plugin can Add featured image thumbnail to WordPress admin columns. It will help you easy to know which post is attached the featured image. Add click the thumbnail will popup preview the full image.
It also support custom posts.
<a href="http://www.wphigh.com/portfolio/admin-featured-thumbnail-wordpress-plugin" rel="nofollow ugc">Feedback Admin Featured Thumbnail</a>

Admin Featured Thumbnail

Add post thumbnails to admin list of posts.

Tiny Default Thumbnail vs Admin Featured Thumbnail