glowrocks

For posts and pages with no featured image, and no images associated with the entry, a random image is selected from the media library and set as the featured image.
The plugin currently does not test for images associated with the entry.
Instead, install and run the Easy Add Thumbnail plugin (https://wordpress.org/plugins/easy-add-thumbnail/).
That plugin will set the featured image on all entries that both have no featured image AND have an image associated with the post.
What is left is entries without featured images and without any images.
This plugin provides a random image from the sites media library so that index pages look more interesting (and possibly confusing/humorous depending on which image is randomly selected.)
There is a notice at the bottom of each post the plugin has updated noting the random image. In a future release, this note will be optional via the standard user interface, but for now one has to edit the plugin and remove the last “filter” line. This notice is not displayed if the plugin is removed.

Random Auto Featured Image

For posts/pages with no featured image, & no images associated with the entry, a random image is selected from media library & set as featured image.

Shellbot

Sometimes you need a proper image gallery to display particular images, and there 
are plenty of plugins for that. Easy Image Display is for those other 
times, when all you need is an easy way to display some random images, or X latest/oldest 
images uploaded to your site.
Current features include:
<ul>
<li>Show or hide image captions</li>
<li>Newest, oldest, random and custom sorting options</li>
<li>Include/exclude images based on ID</li>
<li>Widget, shortcode and template tag for maximum flexibility</li>
<li>Display images at various sizes</li>
<li>Control how many images are displayed and in how many columns</li>
<li>Link images to a lightbox, static URL, or remove link entirely</li>
<li>Uses gallery shortcode so will always fit your theme</li>
</ul>
Features soon to be added:
<ul>
<li>Filter images by attachment status</li>
<li>Slideshow layout</li>
<li>Custom image sizes</li>
</ul>
If you’d like to support the ongoing development of this plugin, please <a href="http://patreon.com/shellbot" title="Support this plugin on Patreon" rel="nofollow ugc">take a look at my Patreon page</a>.
Usage
Easy Image Display provides 3 ways of displaying images; widget, shortcode and template tag. Each method accepts the same options and will result in the same display.
Widget
The Easy Image Display widget is the easiest way to display your images. The basic settings allow you to control image size, order and number. More advanced settings are collapsed by default to provide a simple uncluttered interface.
Choose your options, hit save, and rejoice.
Shortcode
To display images inside a post or page rather than a widget area, you need a shortcode.
Default settings:
<pre><code>[sb_easy_image]
</code></pre>
Custom settings:
<pre><code>[sb_easy_image num="1" order="random" link="lightbox"]
</code></pre>
Template tag
The template tag is available for users who are confident in adding code to theme files, and need to display images outside of the widget areas or main content area. The following function can be added anywhere in your theme files.
Default settings:
<pre><code><?php sb_easy_image(); ?>
</code></pre>
Custom settings:
<pre><code><?php

$args = array(
 "num" => "1",
 "order" => "random",
 "link" => "lightbox",
);

sb_easy_image( $args );

?>
</code></pre>
For full list of parameters see <a href="http://codebyshellbot.com/wordpress-plugins/easy-image-display/" title="Easy Image Display" rel="nofollow ugc">the plugin release page</a>

Easy Image Display

A handy plugin if you need such a function. Very well conceived and useful options. I like the ability to show column of images in widget and to choose with images size to choose.



Very good

Display newest, oldest or random images uploaded to your site.

Random Auto Featured Image vs Easy Image Display