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.

8MediaCentral

Watermark WP Image Protect allows you to watermark all the images on your site. Unlike other watermarking techniques and plugins, the original images are unaffected and you do not need to edit or re-upload the images, it is done automatically for you on-the-fly.
Out of the box WP Image Protect has all these capabilities:
<ul>
<li>Apply text watermarks to all of your site in seconds (new and existing uploads) </li>
<li>Set the text, font, colour, size and background of the Watermark</li>
<li>Specify threshold to apply watermarks (to exclude thumbnails as required)</li>
<li>Exclude individual images from Watermarking with the media library</li>
<li>Alter, reposition or remove all Watermarks in seconds through your WordPress administration panel</li>
<li>View Image Statistics (goto Media > Library)</li>
</ul>
Please raise any support queries on the support forum.
<a href="http://8mediacentral.com/developments/wp-image-protect-watermark-wordpress-images-plugin/" rel="nofollow ugc">Add the WP Image Protect Premium Pack</a> for even more powerful features such as:
<ul>
<li>Images as Watermarks</li>
<li>Watermark Transparency</li>
<li>Hotlink Prevention</li>
<li>Supercharged Performance</li>
<li>Variable Text Watermarks</li>
<li>Additional Fonts</li>
<li>Premium Support</li>
</ul>
Video Demonstration
A short video showing how to get started with Watermark WP Image Protect:
<iframe loading="lazy" class="youtube-player" width="750" height="422" src="https://www.youtube.com/embed/ElAJo-ojvIc?version=3&rel=1&showsearch=0&showinfo=1&iv_load_policy=1&fs=1&hl=en-US&autohide=2&wmode=transparent" allowfullscreen="true" style="border:0;" sandbox="allow-scripts allow-same-origin allow-popups allow-presentation allow-popups-to-escape-sandbox"></iframe>
Some of the features included in the premium pack:
<iframe loading="lazy" class="youtube-player" width="750" height="422" src="https://www.youtube.com/embed/sZcToOC96CE?version=3&rel=1&showsearch=0&showinfo=1&iv_load_policy=1&fs=1&hl=en-US&autohide=2&wmode=transparent" allowfullscreen="true" style="border:0;" sandbox="allow-scripts allow-same-origin allow-popups allow-presentation allow-popups-to-escape-sandbox"></iframe>

Watermark WP Image Protect

Watermark WP Image Protect is an on-the-fly image watermarking plugin for WordPress.

Bulk Watermark vs Watermark WP Image Protect