kdmurray

This plugin will generate an tag for a random image selected from a specified folder.
<h3>Setup Instructions</h3>
<ol>
<li>Extract randomImage.php into your wp-content/plugins folder (or a subfolder)</li>
<li>Activate the plugin in WordPress</li>
<li>On the options screen, select the “Random Image” menu</li>
<li>Fill in the values for your physical and http paths</li>
<li>Select scaling options (optional)</li>
<li>Add some code to whatever page you want to display the image. This is a great way to 
customize the header image for your wordpress installation. The plugin will look in 
the folder and randomly select a header image to display.</li>
</ol>
<h3>Sample Code</h3>
By placing code like the following in your header, it will create an image tag for you 
based on the images in the specified folder.
<?php 
 if (function_exists(‘generateRandomImgTag’)) 
 { 
 generateRandomImgTag(); 
 } 
 ?>
<!– 
The lines above are for the HTML documentation (online)
–>
This code will ensure that the function exists (ie the plugin is active and working) and 
call it if it’s working correctly. If the function is missing, or the plugin has been 
removed then the call will be ignored, and no errors will result.
<h3>Feedback</h3>
kdmurray.at.kdmurray.dot.net

Random Image Selector

This plugin will generate an  tag for a random image selected from a specified folder.

MyWebsiteAdvisor

ChrisHurst

This plugin allows you to Automatically add a watermark to all images as they are uploaded to the WordPress Media Library. 
The plugin uses PNG watermark images with transparency for precise control over the appearance of the watermarks. 
This plugin also supports simple text watermarks with adjustable color, size and transparency. 
The plugin can be configured to apply ‘text and image’, ‘text only’ or ‘image only’ watermarks. 
The user friendly settings page allows for control over the appearance of your watermark. 
The watermark preview feature allows for easy testing of the plugin settings. 
The watermark size is controlled as a percentage of the target image, 50% means the watermark will be half the width of the target image.
<a href="http://MyWebsiteAdvisor.com/plugins/signature-watermark/" rel="nofollow ugc">Upgrade to Signature Watermark Ultra</a> for advanced 
watermark features including:
<ul>
<li>Manually Apply Watermarks to Images Previously Uploaded</li>
<li>Fully Adjustable Text and Image Watermark Positions</li>
<li>Adjustable JPEG Image Output Quality</li>
<li>Highest Quality Watermarks using Image Re-sampling rather than Re-sizing</li>
<li>Lifetime Priority Support and Update License</li>
</ul>
Check out the <a href="http://www.youtube.com/watch?v=pg3WvPBliM4&hd=1" rel="nofollow ugc">Signature Watermark Plugin for WordPress Video Tutorial</a>:
<iframe loading="lazy" title="Signature Watermark for WordPress Video Tutorial" width="750" height="422" src="https://www.youtube.com/embed/pg3WvPBliM4?feature=oembed" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>
Developer Website: http://MyWebsiteAdvisor.com/
Plugin Support: http://MyWebsiteAdvisor.com/support/
Plugin Page: http://MyWebsiteAdvisor.com/plugins/signature-watermark/
Compare Watermark Plugins: http://MyWebsiteAdvisor.com/tools/wordpress-plugins/watermark-plugins-for-wordpress/
Video Tutorial: http://mywebsiteadvisor.com/learning/video-tutorials/signature-watermark-tutorial/
Requirements:
<ul>
<li>PHP v5.0+</li>
<li>WordPress v3.3+</li>
<li>GD extension for PHP</li>
<li>FreeType extension for PHP</li>
</ul>
To-do:

Signature Watermark

Automatically watermark images as they are uploaded to the WordPress Media Library using Both Images and Text.

Random Image Selector vs Signature Watermark