Ethan Allen

A simple and easy way to add featured images in your site’s RSS feed with customizable sizing options.
Adds featured images to Mailchimp emails, Infusionsoft, Hubspot, Constant Contact, Zoho, Feedburner, Bloglovin’, Feedly, and other services that use RSS feed data.
Works great with Mailchimp’s RSS-to-Email campaigns, allowing you to be more creative and get the most value from your email newsletters. You can even set the xml encoding of your RSS feed. (the default setting is UTF-8).
For more information on setting up and using RSS with Images, view the documentation <a href="https://endif.media/userdocs/setting-up-and-using-rss-with-images/" rel="nofollow ugc">here</a>.
note: RSS with Images will not add already existing images to your feed. Once the plugin is activated, any new image added to a post will be included in the feed.
<a href="https://wordpress.org/support/view/plugin-reviews/rss-with-images?filter=5#postform" rel="ugc">Rate this plugin</a>, I would LOVE the feedback!
ENJOY!

RSS with Images

Had to leave my first ever rating for a Wordpress plugin because I felt the current 3/5 star rating was extremely unfair. I've used this plugin on a production site for over a year (to integrate with Mailchimp RSS campaigns) and it's worked flawlessly.



Does what it says on the tin

Seamlessly adds featured images to your RSS feed with customizable sizing options.

xaraartech

Abuzer

Adds functionality to search images from post page and attach as featured image. 
You will require to create an API key on bing for search API. 
GOTO: https://azure.microsoft.com/en-us/services/cognitive-services/bing-image-search-api/ or https://dev.cognitive.microsoft.com/docs/services/56b43f0ccf5ff8098cef3808/operations/571fab09dbe2d933e891028f 
And generate your “Ocp-Apim-Subscription-Key”

External featured image from bing

Adds functionality to search images from post page and attach as featured image.

RSS with Images vs External featured image from bing