ChrisHurst

MyWebsiteAdvisor

This plugin allows you to watermark your previously uploaded images using a PNG image file with transparency as well as text signature. 
The user friendly settings page allows for control over the appearance of your watermark. 
You can set your watermarks to always be a specific percentage of the target image. 
This plugin will add the watermarks to ALL of the images in your WordPress uploads directory.
Please BACK UP all of your uploads via FTP before using this plugin!
<a href="http://mywebsiteadvisor.com/plugins/bulk-watermark/" rel="nofollow ugc">Upgrade to Bulk Watermark Ultra</a> for advanced 
watermark features including:
<ul>
<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=XkFXBjfzw2I&hd=1" rel="nofollow ugc">Bulk Watermark Plugin for WordPress Video Tutorial</a>:
<iframe loading="lazy" title="Bulk Watermark for WordPress Tutorial" width="750" height="422" src="https://www.youtube.com/embed/XkFXBjfzw2I?feature=oembed" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>
Developer Website: http://MyWebsiteAdvisor.com/
Plugin Support: http://MyWebsiteAdvisor.com/support/
Plugin Page: http://mywebsiteadvisor.com/plugins/bulk-watermark/
Compare Watermark Plugins: http://MyWebsiteAdvisor.com/tools/wordpress-plugins/watermark-plugins-for-wordpress/
Video Tutorial: http://mywebsiteadvisor.com/learning/video-tutorials/bulk-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:

Bulk Watermark

Adds an image and/or text watermark to all uploaded images, using PNG images with transparency.

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.

Bulk Watermark vs Image Watermark