Related Posts by WPBrigade is The Best Customizable plugin, that nicely displays related posts thumbnails under the post.

Adnan

WPBrigade

<a href="https://wpbrigade.com/wordpress/plugins/related-posts/?utm_source=related-posts-lite&utm_medium=readme&utm_campaign=pro-upgrade-rp" rel="nofollow ugc">Related Posts by WPBrigade</a> will add related posts thumbnails after the post. This Related Posts Plugin allows to customize thumbnail sizes, display settings and type of relation.
By default it uses generated by WordPress thumbnail for the first image appeared in the post, that was uploaded on the server with sizes as set in Media settings. You can select between ‘thumbnail’ and ‘medium’ size options. In addition if your theme supports Post Thumbnails feature introduced in WordPress 2.9 you can specify custom thumbnail size. You can also specify post custom field name to be used as thumbnails source.
Thumbnails are arranged in columns under the post with related posts title/excerpt under each post thumbnail. Colors of background, border, text, text sizes, background on mouse over, title and excerpt length can be customized. See screenshot.
You can specify number of related posts to display, start date, categories to show on and to include, top text, style settings, default image URL. You can select type of relation – categories, tags, categories and tags, random or custom taxonomies. You can specify where to display related posts – choose page type (main or single), post type and select categories. You can turn off automatic appending to the end of post and use <?php get_related_posts_thumbnails(); ?> php tag in the Loop of your theme. Related Posts thumbnails sidebar widget is also available. You can use [related-posts-thumbnails] shortcode in the post body.
** This Related Posts plugin has Gutenberg block **
Contributions:
<ul>
<li>Thanks to <a href="https://adnan.pk/?utm_source=related-posts-lite&utm_medium=readme&utm_campaign=xp" rel="nofollow ugc">Adnan</a> for giving life to this plugin.</li>
</ul>
Translations:
<ul>
<li>This plugin has Russian version</li>
<li>Thanks to <a href="https://www.li-an.fr/wpplugins/" rel="nofollow ugc">Li-An</a> this plugin has French version</li>
<li>Thanks to <a href="https://gidibao.net/" rel="nofollow ugc">Gidibao</a> this plugin has Italian version</li>
<li>Thanks to <a href="https://www.kuzublog.com/" rel="nofollow ugc">Kuzu</a> this plugin has Turkish version</li>
<li>Thanks to <a href="https://www.meinblog.de/" title="MeinBlog.de - eigenes Tagebuch" rel="nofollow ugc">Mirko</a> this plugin has German version</li>
<li>Thanks to <a href="https://bejana.com/" rel="nofollow ugc">Bejana</a> for Indonesian translation</li>
</ul>
Related Links:
<ul>
<li><a href="https://wpbrigade.com/wordpress/plugins/related-posts/?utm_source=related-posts-lite&utm_medium=readme&utm_campaign=pro-upgrade-rp" title="Related Posts Thumbnails Plugin for WordPress" rel="nofollow ugc">Plugin Homepage</a> – see possible problems and solutions.</li>
<li><a href="https://wpbrigade.com/wordpress/plugins/loginpress-pro/?utm_source=related-posts-lite&utm_medium=readme&utm_campaign=pro-upgrade" title="Rebrand your WordPress login page with LoginPress" rel="nofollow ugc">Rebrand your WordPress login page with LoginPress</a></li>
</ul>

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