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.

sewpafly

To meet the needs of themes where the post-thumbnails have random and capricious sizes (which causes wordpress to crop images simply from the middle (either chopping off the top and bottom or chopping off the sides), this plugin attempts to give the users an interface to manually fix those thumbnail and random images.

Post Thumbnail Editor

Does not work

Fed up with the lack of automated tools to properly crop and scale post thumbnails? Maybe this plugin can help.

Multisite Featured Image vs Post Thumbnail Editor