Truefy

<a href="https://embed.truefy.ai/" rel="nofollow ugc">Truefy Embed</a> allows you to invisibly watermark images uploaded to the WordPress Media Library or a WordPress Post. 
The Plugin will also directly sync the changes in Image Caption from WordPress to Truefy Embed 
Once uploaded, you can view them in the Image library in Truefy Embed Website, where you can add or edit the critical details like Image Capture Datetime, Publisher Details etc.
For more information, check out <a href="https://embed.truefy.ai/integrations/wordpress" rel="nofollow ugc">plugin page</a> or email us at support@truefy.ai
You can check Truefy Embed’s Terms of Service at <a href="https://embed.truefy.ai/legal/tos" rel="nofollow ugc">ToS Page</a>
<h4>Features include:</h4>
<ul>
<li>Auto Invisible Watermarking – Images uploaded to Media Library or a Post can be automatically invisibly watermarked</li>
<li>Manual Invisible Watermarking/De-Watermarking – Images can be manually watermarked, and even be de-watermarked</li>
<li>Image Caption Syncing – Captions added for Images in Media Library or Post Caption, are directly synced to Truefy Embed Servers</li>
</ul>

Truefy Embed

Truefy Embed's proprietary AI invisible watermarking technology secures your images by allowing you to add critical details directly into the pix …

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

Truefy Embed vs Simple Watermark