tepelstreel

The RSS Image Feed doesn’t create a feed of images, but ataches the first image of the post to your feeds. Normally only the content has images showing. With our plugin there will be a clickable image even in the excerpt and in the content there will be only one image instead of all the images of the post. Since version 2.2 it works as a multisite plugin as well.
The plugin was tested up to WP 4.5 It should work with versions down to 2.7 but was never tested on those.

RSS Image Feed

The RSS Image Feed adds the first image of a post to your feeds, even in firefox and even if you only display the excerpt.

J0SiE

Created to help those people who don’t like to edit code in template files (or are too lazy to do that). 
Just activate the plugin and it will automatically show the_excerpts in your homepage, archives and search results. 
It tries to display your custom excerpt text and if it doesn’t find it it will show an automatically generated excerpt. 
You can also define excerpt length, custom read more link and attach a thumbnail.

Auto Excerpt everywhere

Thanks to author for creating this plugin. 
It's works out of box. And working fine at WordPress Version 4.6.1


Works out of the box on WP Version 4.6.1

The plugin automatically displays excerpts instead of full post contents in your blog. Custom excerpts and generated excerpts supported.

RSS Image Feed vs Auto Excerpt everywhere