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.

Christian Foellmann

Ankit Pokhrel

Dynamically adds multiple featured image or multiple post thumbnail functionality to your page, posts and custom post types. This plugin provides you an interface to add any number of featured image as you want without writing a single line of code. These featured images can then be collected by the various theme functions.
Overview
Dynamic Featured Image enables the option to have MULTIPLE featured images within a post or page. 
This is especially helpful when you use other plugins, post thumbnails or sliders that use featured images. 
Why limit yourself to only one featured image if you can do some awesome stuffs with multiple featured image? 
DFI allows you to add different number of featured images to each post and page that can be collected by the various theme functions.
<blockquote>
A NOTE ABOUT SUPPORT: We’re here to help troubleshoot bugs, but please don’t set expectations early as the support forums at WordPress.org are only checked once in a while.
</blockquote>
How it works? 
1. After successfull plugin activation go to <code>add</code> or <code>edit</code> page of posts or pages and you will notice a box for second featured image. 
2. Click <code>Set featured image</code>, select required image from “Dynamic Featured Image – Media Selector” popup and click <code>Set Featured Image</code>. 
3. Click on <code>Add New</code> to add new featured image or use <code>Remove</code> link to remove the featured image box. 
4. You can then get the images by calling the function <code>$dynamic_featured_image->get_featured_images([$postId (optional)])</code> in your theme. (<a href="https://github.com/ankitpokhrel/Dynamic-Featured-Image/wiki" title="Documentation for current version" rel="nofollow ugc">Click here for details</a>) 
5. The data will be returned in the following format.
<pre><code>array
 0 => 
 array
 'thumb' => string 'http://your_site/upload_path/yourSelectedImage.jpg' (length=50)
 'full' => string 'http://your_site/upload_path/yourSelectedImage_fullSize.jpg' (length=69)
 'attachment_id' => string '197' (length=3)
 1 => 
 array
 'thumb' => string 'http://your_site/upload_path/yourSelectedImage.jpg' (length=50)
 'full' => string 'http://your_site/upload_path/yourSelectedImage_fullSize.jpg' (length=69)
 'attachment_id' => string '198' (length=3)
 2 => ...
</code></pre>
Resources 
1. <a href="https://github.com/ankitpokhrel/Dynamic-Featured-Image/wiki" title="Documentation for current ver." rel="nofollow ugc">Detail Documentation</a>. 
2. <a href="https://stackoverflow.com/questions/tagged/dynamic-featured-image" title="StackOverflow Tag" rel="nofollow ugc">StackOverflow Tag</a>.
MultiSite Info 
You can use <code>Network Activate</code> to activate plugin for all sites on a single install. It is only available on the Network admin site not anywhere else. 
Simple <code>Activate</code> activates for the site you are currently on. These will be permitted to be activated or deactivated on ANY blog.
While deleting the plugin from the <code>Network</code> be sure that the plugin is deactive in all installation of your WordPress network.
Contribute 
If you’d like to check out the code and contribute, join us on <a href="https://github.com/ankitpokhrel/Dynamic-Featured-Image" title="View this plugin in github" rel="nofollow ugc">Github</a>. 
Pull requests, issues, and plugin recommendations are more than welcome!

Dynamic Featured Image

Works fine!

Dynamically adds multiple featured image (post thumbnail) functionality to posts, pages and custom post types.

Multisite Featured Image vs Dynamic Featured Image