ulfben

This plugin adds an “Use as Featured Image”-action to the Media Library. Very useful if you need to set the post thumbnail / featured image for a lot of posts.
<a href="https://wordpress.org/extend/plugins/bulk-select-featured-image/screenshots/" rel="ugc">A picture says more than a thousand words</a>.
//<a href="https://www.ulfbenjaminsson.com/" rel="nofollow ugc">Ulf Benjaminsson</a> 
Copyright (C) 2012 Ulf Benjaminsson (hello at my full name dot com).
This program is free software; you can redistribute it and/or modify 
it under the terms of the GNU General Public License as published by 
the Free Software Foundation; either version 2 of the License, or 
(at your option) any later version.
This program is distributed in the hope that it will be useful, 
but WITHOUT ANY WARRANTY; without even the implied warranty of 
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 
GNU General Public License for more details.
You should have received a copy of the GNU General Public License 
along with this program; if not, write to the Free Software 
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

Bulk-Select Featured Image

Allows you to select Featured Image / post thumbnail for your posts directly from the media library view.

Mohamed Tawfik

This plugin let you add a featured image to a post using external URL.
You can use images from Flickr, google images… etc just in one click. 
No need to download the image and re-upload it again.
The image will be processed and thumbnails will be generated just like if you uploaded the image your self from your PC.
It is working with native and custom post types.
It is available now in two languages:
1- English 
2- Arabic
You can translate it to any languages.

WK URL 2 WP Thumb

This plugin let you add a featured image to a post using external URL.

Bulk-Select Featured Image vs WK URL 2 WP Thumb