William Arin

AquaMark is a full-featured, professional solution for applying image watermarks to your media uploads. 
Built with a modern, robust architecture, it provides extensive control over the appearance and placement of your watermark, ensuring your brand is consistently represented across your site. 
The plugin automatically uses the best available image processing library on your server (Imagick for quality, GD for compatibility) to deliver excellent results.
<h4>Core Features</h4>
<ul>
<li>Selectable Watermark Image: Choose any image from your Media Library to use as a watermark.</li>
<li>Precise Positioning: Place your watermark in any one of nine grid positions (top-left, middle-center, bottom-right, etc.).</li>
<li>Fine-Tuned Offset: Adjust the watermark’s final position with pixel (px) or percentage (%) based X and Y offsets.</li>
<li>Flexible Sizing: Control the watermark’s size with pixel (px) or percentage (%) based width and height. Supports auto-scaling.</li>
<li>Opacity Control: Set the transparency of your watermark from 0% (fully transparent) to 100% (fully opaque).</li>
<li>Advanced Blend Modes: Go beyond simple overlays with Photoshop-like blend modes, including Normal, Multiply, Screen, and Overlay.</li>
<li>Target Specific Image Sizes: Choose exactly which registered image sizes should receive the watermark (e.g., thumbnail, medium, large).</li>
<li>Image Driver Selection: Automatically uses the best image library available (Imagick or GD), with a manual override option for advanced users.</li>
<li>Destructive Action Warning: The plugin warns you if you choose to apply the watermark to the ‘full’ size image, as this is a permanent, destructive action.</li>
<li>Regenerate Watermarks: Easily apply new settings to existing images via a “Regenerate Watermarks” bulk action in the Media Library.</li>
<li>Remove Watermarks: Remove watermarks from existing images via a “Remove Watermarks” bulk action in the Media Library.</li>
<li>Developer Friendly: Includes WordPress actions and filters for programmatic extension and customization.</li>
<li>Modern & Conflict-Free: Built with modern PHP and scoped dependencies to prevent conflicts with other plugins.</li>
</ul>
<h3>Developer Documentation</h3>
The plugin includes a variety of actions and filters for programmatic customization. For detailed documentation and code examples, please see the <code>DEVELOPER.md</code> file included with the plugin.

AquaMark

Add a custom watermark to your images in the WordPress media library with powerful controls and blending modes.

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" class="youtube-player" width="750" height="422" src="https://www.youtube.com/embed/pg3WvPBliM4?version=3&rel=1&showsearch=0&showinfo=1&iv_load_policy=1&fs=1&hl=en-US&autohide=2&hd=1&wmode=transparent" allowfullscreen="true" style="border:0;" sandbox="allow-scripts allow-same-origin allow-popups allow-presentation allow-popups-to-escape-sandbox"></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.

AquaMark vs Signature Watermark