ChrisHurst

MyWebsiteAdvisor

This plugin allows you to Automatically displays a watermark on images which have been hotlinked as they are viewed on the Hotlinkers Website. 
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. 
Watermarks are non-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!
<a href="http://MyWebsiteAdvisor.com/tools/wordpress-plugins/watermark-hotlink-protection/" rel="nofollow ugc">Upgrade to Watermark Hotlink Protection Ultra</a> for advanced 
watermark features including:
<ul>
<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/watermark-hotlink-protection/
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:

Watermark Hotlink Protection

Displays a watermark on images which have been hotlinked

daxiawp

Automatically add a picture watermark, can select text or pictures are two types. 自动给图片添加水印，可选择文本或图片两种类型。 
详情：<a href="http://www.daxiawp.com/dx-watermark.html" rel="nofollow ugc">http://www.daxiawp.com/dx-watermark.html</a>
<h3>Arbitrary section 1</h3>

DX-Watermark

The pictures automatically add watermark. 图片自动添加水印.

Watermark Hotlink Protection vs DX-Watermark