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 viewed on your WordPress Website. 
Watermarks are not permenant, original images are not edited. 
The plugin maintains a cached copy of the watermarked image, which can be cleared and regenerated at any time!
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 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.
This plugin needs to add to your .htaccess file, and will not work if you do not have a .htaccess file or mod_rewrite.
NOTE: 
This plugin may have a slight impact on the performance of your web server, use of the Included Basic Caching System is Highly Recommended! 
The premium version of this plugin also includes an Advanced Cache System which performs nearly identical to when the plugin is disabled.
<a href="http://MyWebsiteAdvisor.com/tools/wordpress-plugins/simple-watermark/" rel="nofollow ugc">Upgrade to Simple Watermark Ultra</a> for advanced 
watermark features including:
<ul>
<li>Improved Performance with Advanced Cache</li>
<li>Fully Adjustable Image Watermark Position</li>
<li>Fully Adjustable Text Watermark Position</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>
Developer Website: http://MyWebsiteAdvisor.com/
Plugin Support: http://MyWebsiteAdvisor.com/support/
Plugin Page: http://MyWebsiteAdvisor.com/tools/wordpress-plugins/simple-watermark/
Requirements:
<ul>
<li>PHP v5.0+</li>
<li>WordPress v3.3+</li>
<li>GD extension for PHP</li>
<li>FreeType extension for PHP</li>
<li>.htaccess file and mod_rewrite</li>
</ul>
To-do:

Simple Watermark

Automatically watermark images as they are viewed

Random Image Selector vs Simple Watermark