by Vincent Dubroeucq on WordPress.org
Allows you to add a default featured image to posts. Just add a default image in your customizer settings !
Find your default featured image setting under Tiny Default Thumbnail section in the WordPress Customizer tool.
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 !