Igor Benic

Multisite Featured Image changes the box of the featured image for all sites. It can be used also in a single instance of WordPress and not a MU installation.
This plugin changes the box in the way that the default pop-up is replaced with the classic Media Uploader where you can choose images. Images From URL do work.
For a greater Multisite experience you can combine this plugin with the <a href="https://wordpress.org/plugins/network-shared-media/" rel="ugc">Network Shared Media plugin</a> and have a complete Media Sharing site.
Read about it on this <a href="http://siderrz.com/wordpress-multisite-shared-featured-image/" rel="nofollow ugc">article</a>.
<h4>Features</h4>
<ul>
<li>Using WordPress Media Uploader to set Featured Image</li>
<li>You can set an image from URL</li>
<li>Images from URL will be downloaded into the WordPress Media and it can be used for anything else inside WordPress</li>
<li>Downloaded images are saved in every registered image size </li>
<li>You can set the Main site on which you will download the images in a MU installation</li>
</ul>

Multisite Featured Image

Multisite Featured Image changes the box of the featured image so that you can use the classic Media Uploader also with Network Shared Media.

Sanny Srivastava

Are you tired of manually configuring a default featured image each time you publish a page, post, or custom post type? Do you desire a default featured image to automatically serve as a thumbnail whenever you publish or update your post/page?
Look no further!
This plugin provides a convenient solution to set a default thumbnail image effortlessly for all your posts, pages, or custom post types. Select or upload any image from your media library with ease.
Access the settings via the WordPress Dashboard under Settings => “SNY Auto Featured Image” (admin menu).
Quick Setup:
<ul>
<li>Choose/upload an image from the media library.</li>
<li>Specify categories.</li>
<li>Define the post types.</li>
</ul>
Please note that this plugin automatically assigns a thumbnail when a post is published or modified, but only if the post lacks a featured image.

SNY Auto Featured Image

Automatically set a default featured image for posts, pages, or custom post types when none is assigned.

Multisite Featured Image vs SNY Auto Featured Image