Anuar

Not all themes work the same way, and sometimes switching themes can lead to a lot of headaches. If you’ve previously used a theme that supports featured images and displays them on single post views, you probably want to ensure that these images are still shown if you switch to a theme that doesn’t show featured images here, without editing all of your old content.
This plugin automatically displays featured images at the top of the content area on single post views. It doesn’t check whether your theme displays them, so you’ll get double featured images if it does. It works via a filter, so if you ever switch themes again to one that does support featured images on single views, you can deactivate this plugin and things will go right back to normal. No information is saved in the database and no additional special image sizes are generated in this plugin.
<h4>Possible Core Material</h4>
This plugin may be material for WordPress core if it were to display featured images that exist when the current theme doesn’t support featured images. While this would reduce the potential for content loss, it would also have a significant affect on existing content.

Featured Image in Content

Not all themes work the same way, and sometimes switching themes can lead to a lot of headaches. If you've previously used a theme that supports  …

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.

Featured Image in Content vs Bulk-Select Featured Image