Bill Erickson

When you upload an image, WordPress will automatically scale/crop it to many different sizes. If you’re not happy with the auto-crops, use this plugin to upload an alternative image.
If you have images showing up in your theme already, there’s nothing you need to do after activating this plugin. All WordPress functions that provide the thumbnail should now automatically work with your override image.
This plugin will add a metabox to every post type and allow you to modify every image size (built-in and custom ones added using add_image_size). You can use two filters to change these (image_override_post_types and image_override_sizes). For examples, see the documentation.
<a href="https://github.com/billerickson/Image-Override/wiki" rel="nofollow ugc">Documentation</a>
No support will be provided by the developer

Image Override

Allows you to override WordPress' auto generated thumbnails.

Jordy Meow

RSS Featured Image adds the featured image into your RSS feed (in the media:content). It works nicely with Mailchimp (|RSSITEM:IMAGE|). In fact, it basically does the same thing as another (and more famous) plugin but without cluttering your WordPress Admin. This is a simple task, and I believe it should be invisible and run peacefuly in the background, with no impact on the UI and the overall WordPress performance.
<h3>Usage</h3>
By default, the size of the image is “large”. I think it would be a shame to add new options to your WordPress admin only for this, so if you want to change the size, I propose you a filter 🙂 You can include some code in your functions.php to take care of this. This is how you can use it:
function thumbnail_size_for_rss( $default ) { 
 return ‘thumbnail’; 
} 
add_filter( ‘rfi_rss_image_size’, ‘thumbnail_size_for_rss’, 10, 1 );

RSS Featured Image

Add the featured image into your RSS feed (in the media:content). Works nicely with Mailchimp (|RSSITEM:IMAGE|). Light and simple, no options, no clut …

Image Override vs RSS Featured Image