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 !

Pascal Birchler

required

Ulrich

Silvan Hagen

With this plugin, an MRSS namespace is added to the site’s RSS feed to include each post’s thumbnail.
WP Feed Post Thumbnail is very lightweight and only adds two small options under Settings -> Reading.
<h3>Contribute</h3>
If you would like to contribute to this plugin, report an issue or anything like that, please note that we develop this plugin on <a href="https://github.com/wearerequired/required-wp-feed-post-thumbnail" rel="nofollow ugc">GitHub</a>.
Developed by <a href="https://required.com/" title="Team of experienced web professionals from Switzerland & Germany" rel="nofollow ugc">required</a>

Feed Post Thumbnail

Tried refreshing permalinks, saving settings on the General settings page you've added the two checkboxes to, nothing makes a difference. No post thumbnail in the feeds...

Update! And then it started working!

I'm guessing this may have had something to do with either my hosting's caching or possibly even just my own browser cache. Works like a dream, thank you!

Not adding anything...

Adds MRSS namespace to the feed and uses post-thumbnail as media element in the feed. Settings available under Settings -> Reading.

Tiny Default Thumbnail vs Feed Post Thumbnail