Nick Halsey

This plugin creates a fullscreen slideshow that displays randomly-selected pictures from your media library. Designed to display pictures related to your business/organization in the background at an event or in your office, there is no need to configure any settings or controls. Image captions/descriptions are automatically displayed as well, and can be configured based on your needs.
Once activated, you can view the slideshow by visiting <code>http://yourdomain.com/slideshow</code>. All JPEG images will be displayed (since .jpg is best for pictures, while .png and .gif are typically used for graphics).
Please note that it is not currently possible to pause the slideshow or go back; the slideshow is not designed for personal viewing. However, clicking/tapping on the image will open its attachment page in a new tab, allowing images to be contextualized or edited easily.
The slideshow can also be embedded into your site via a widget or a shortcode.
You can control some options by adjusting the url of the slideshow. Parameters are controlled via query string (and widget options and shortcode attributes).
<ul>
<li><code>size</code> is the size of the image to load, either <code>thumbnail</code> (discouraged), <code>medium</code>, <code>large</code>, <code>full</code>, or <code>auto</code>, which uses medium or large depending on <code>wp_is_mobile()</code>.</li>
<li><code>year</code> is the 4-digit numeric year in which the images were published.</li>
<li><code>month</code> is the numeric month in which the images were published (between 1 and 12), typically but not necessarily used in conjunction with <code>year</code>.</li>
<li><code>mode</code> defines a subset of images to use, such as <code>featured</code> for featured images only.</li>
<li><code>captions</code> controls the captions display: either <code>auto</code>, <code>none</code>, <code>title</code>, <code>titlecaption</code>, <code>caption</code>, or <code>description</code>. Caption data is read from the image attachment post and can be updated in the media library.</li>
</ul>
Using all options, for example: 
http://example.com/slideshow?size=full&year=2014&month=4&mode=featured&captions=titlecaption
You can see it in action <a href="http://uscasce.com/slideshow" rel="nofollow ugc">here</a>.

Content Slideshow

This plugin creates a fullscreen slideshow that displays randomly-selected pictures from your media library. Designed to display pictures related to y …

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.

Content Slideshow vs Signature Watermark