Eric Teubert

WordPress automatically discovers enclosures you reference in a post. Use this plugin to stop WordPress from doing that.
All other enclosures will work. Existing enclosures will not be deleted.
<h4>Quick Start</h4>
Activate the plugin. 
Enjoy 🙂

No More Enclosures

WordPress automatically discovers enclosures you reference in a post. Use this plugin to stop WordPress from doing that.

Iuri Moura

This plugin ensures each RSS item has a consistent image:
<ul>
<li>Prepends the post featured image to the feed content (optional).</li>
<li>Adds Media RSS (<code><media:content></code>) and/or <code><enclosure></code> (optional).</li>
<li>Removes emojis in feeds to avoid emoji images.</li>
<li>Fallbacks: first image found in the content or a custom default URL.</li>
<li>Choose the image size (thumbnail, medium, large, full, etc.).</li>
</ul>
No new feed URL is created. It augments the default WordPress RSS feed (<code>/feed/</code>).

Emanda – Featured Image in RSS

Adds the post’s featured image to the default WordPress RSS feed. Optional Media RSS/enclosure, fallbacks, and emoji cleanup.

No More Enclosures vs Emanda – Featured Image in RSS