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.

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.

Bulk-Select Featured Image vs SNY Auto Featured Image