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

dFactory

<a href="http://www.dfactory.co/products/image-watermark/" rel="nofollow ugc">Image Watermark</a> allows you to automatically watermark images uploaded to the WordPress Media Library and bulk watermark previously uploaded images.
For more information, check out plugin page at <a href="http://www.dfactory.co/" rel="nofollow ugc">dFactory</a>, <a href="http://www.dfactory.co/docs/image-watermark/" rel="nofollow ugc">documentation page</a> or plugin <a href="http://www.dfactory.co/support/forum/image-watermark/" rel="nofollow ugc">support forum</a>.
<h4>Features include:</h4>
<ul>
<li>Bulk watermark – Apply watermark option in Media Library actions</li>
<li>Watermark images already uploaded to Media Library</li>
<li>GD LIbrary and ImageMagic support</li>
<li>Image backup functionality</li>
<li>Option to remove watermark</li>
<li>Flexible watermark position</li>
<li>Watermark image preview</li>
<li>Set watermark offset</li>
<li>Select post types where watermark will be aplied to uploaded images or select adding watermark during any image upload</li>
<li>Select from 3 methods of aplying watermark size: original, custom or scaled</li>
<li>Set watermark transparency / opacity</li>
<li>Select image format (baseline or progressive)</li>
<li>Set image quality</li>
<li>Protect your images from copying via drag&drop</li>
<li>Disable right mouse click on images</li>
<li>Disable image protection for logged-in users</li>
<li>.pot file for translations included</li>
</ul>

Image Watermark

Image Watermark allows you to automatically watermark images uploaded to the WordPress Media Library and bulk watermark previously uploaded images.

Simple Watermark vs Image Watermark