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.

Andy Charrington

Easily add background options on a per page/post basis.
Currently the plugin includes the following features-
<ul>
<li>Add a background image</li>
<li>Options for vertical & horizontal repeating</li>
<li>Fade out the bottom edge of your background image</li>
<li>Choose background colour</li>
<li>Child pages of a page with a custom background will inherit the parent page background settings.</li>
</ul>

Background Per Page

Background Per Page allows you to set a custom background per page (or post) as well as set up a default background for all other pages/posts.

Simple Slideshow Background vs Background Per Page