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.

www.gopiplus.com

gopiplus

The Random image gallery with pretty photo zoom WordPress plug-in which allows you to show random image anywhere in your posts, template files or using widgets.
Check official website for live demo <a href="http://www.gopiplus.com/work/2011/12/12/wordpress-plugin-random-image-gallery-with-pretty-photo-zoom/" rel="nofollow ugc">http://www.gopiplus.com/work/2011/12/12/wordpress-plugin-random-image-gallery-with-pretty-photo-zoom/</a>
<a href="http://www.gopiplus.com/work/2011/12/12/wordpress-plugin-random-image-gallery-with-pretty-photo-zoom/" rel="nofollow ugc">Live demo</a> 
<a href="http://www.gopiplus.com/work/2011/12/12/wordpress-plugin-random-image-gallery-with-pretty-photo-zoom/" rel="nofollow ugc">More information</a> 
<a href="http://www.gopiplus.com/work/2011/12/12/wordpress-plugin-random-image-gallery-with-pretty-photo-zoom/" rel="nofollow ugc">User comments and suggestion</a> 
<a href="http://www.gopiplus.com/work/" rel="nofollow ugc">About author</a>
The Random image gallery with pretty photo zoom WordPress plug-in which allows you to show random image anywhere in your posts, template files or using widgets. When you click the image it will create the pretty photo zoom effect. You can upload your images directly into the folder or you can set the existing image folder location; this plugin will automatically generate the perfect thumbnail image based on the mentioned width. This plugin is very useful to showcase images randomly to user.
Plugin configuration
<ul>
<li>Drag and drop the widget</li>
<li>Paste the php code to your php file</li>
<li>Short code for posts and pages</li>
</ul>
http://www.gopiplus.com/work/2011/12/12/wordpress-plugin-random-image-gallery-with-pretty-photo-zoom/
Features of this plugin
<ul>
<li>Simple and easy installation.</li>
<li>This will create thumbnail image.</li>
<li>Display one image on random order.</li>
<li>Pretty photo zoom effect on mouse click.</li>
</ul>

Random image gallery with pretty photo zoom

This plugin which allows you to simply and easily show random image anywhere in your template files or using widgets with onclick pretty photo zoom.

Random Auto Featured Image vs Random image gallery with pretty photo zoom