barteled

Slideshow background adds a full size, smooth transition slideshow to the background of a WordPress site. Images can be selected from the media library or uploaded via drag-and-drop. Every page load will begin at a random position in the image loop so that users are not presented with the same start image every page change.
Additionally, the images maintain their aspects ratios during resize and turn off for mobile users.
This plug-in was conjured up by a nerd at <a href="http://think-bowl.com/" title="It's less of a tank and more of a bowl." rel="nofollow ugc">Think Bowl</a>

Simple Slideshow Background

Display a full size slideshow in the background featuring images from the media library.

AMP-MODE

Scott DeLuzio

Simple Full Screen Background Image will allow you to easily upload and set a full screen image as the background of your website. Images will be automatically scaled with the browser, so regardless of the browser size, the image will always fill the screen, even as the browser is resized live.
Once activated, go to Appearance > Fullscreen BG Image. From here click Choose Image, then either upload from your computer or choose one from the media library. Once you have chosen your image, select the size you wish to insert and click Insert Into Post. A preview of your image will appear below. Now click Save Options 
and view your site. The image should now be applied as a full screen background image.
<h4>Go Pro!</h4>
A greatly enhanced Pro version is <a href="https://fullscreenbackgroundimages.com/downloads/full-screen-background-images-pro/" rel="nofollow ugc">available</a>! Features of the pro version include:
<ul>
<li>Unlimited background images</li>
<li>Post / page-specific background images</li>
<li>Multiple images with fade transitions on pages</li>
</ul>
Learn more about the Pro version <a href="https://fullscreenbackgroundimages.com/downloads/full-screen-background-images-pro/" rel="nofollow ugc">here</a>.

Simple Full Screen Background Image

This plugin provides a simple way to set an automatically scaled full screen background image.

Simple Slideshow Background vs Simple Full Screen Background Image