One Crayon

Markup to Featured Image will automatically generate a featured image when you publish a post, with the intent of allowing you to publish posts with featured images from third-party clients like MarsEdit.
To add a featured image to your post, include one of the following markup variants in your post’s content:
<pre><code><img src="/path/to/image.jpg" data-featured-image="keep" />
<img src="/path/to/image.jpg" data-featured-image="strip" />

</code></pre>
If you use an <code><img></code> element, the values of the <code>data-featured-image</code> attribute specify whether the image should be displayed when the post is shown on your site (<code>keep</code>) or ignored when the post is displayed (<code>strip</code>). The order of attributes in your <code><img></code> tag (and whether you include other attributes, like width/height, title, alt, etc.) doesn’t matter. You can make it as complicated or simple as you like.
If the post already has a featured image, the plugin will do nothing (version 1.0 does not allow updating the thumbnail by updating the markup).

Markup to Featured Image

Automatically set the featured image (formerly the post thumbnail) for a post based on custom markup in the body text.

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.

Markup to Featured Image vs Feed Post Thumbnail