Strawberry Jellyfish

Easily create full screen image backgrounds and fading slideshows that stretch 
and adapt to the size of your page.
You can either use it as a global “cover” style background that will be 
displayed on all pages and posts of your WordPress website or you can give 
individual posts or pages including custom post types their own specific 
background – great for giving parts of a website a whole different look.
Jellyfish Backdrop makes fullscreen background slideshows easy by allowing 
you to assign multiple backgrounds to any page or post.
<ul>
<li>Unlimited number of post and slideshows.</li>
<li>Create different slideshows or backgrounds or different areas of your site.</li>
<li>Easy to use admin panels with sortable images and media library integration.</li>
<li>Display images in any page element allowing slideshows anywhere, not just as 
a background!</li>
</ul>
<h4>Demo</h4>
See the plugin homepage for demos and full details: 
http://strawberryjellyfish.com/wordpress-plugins/jellyfish-backdrop/
<h3>Usage</h3>
Visit the settings page to set up the global and default options. Here you’ll 
be able to set up a default background image that will be displayed on every 
page of your blog, enable or disable the global background or individual post 
and page background support as well as set up the default options.
To add a unique background image or slideshow to a specific post or page, 
first make sure that in the Enable Page and Post Type Slideshows section 
on the setting page, you check any post types you want to allow slideshows 
to appear on. You’ll now find a new area on the post / page edit screens 
where you can add images to the Backdrop Slideshow and alter fade time, 
slide display time and where the images will appear. Jellyfish Backdrop uses 
the WordPress image uploader and Media Library, so it’s easy to choose the 
images you want to use. You can also reorder the images by dragging. 
Once you’ve finished adding and arranging your images, be sure to save the 
post or your changes will not be saved.
Page / Post backgrounds will override the default background so it’s possible 
to define one background to be used site wide and another on a specific page.
By default images are shown as the main page background (body), however you 
can make the images appear as backgrounds to other areas of the page by 
supplying any valid element id or class name in the Container field on the 
admin page. eg. #main, .header

Jellyfish backdrop

Fullscreen background images and background slideshows on any WordPress post or page. Easily upload and select images using the media library.

Demis Patti

flavor

cbParallax lets you add custom background images with a vertical or horizontal parallax effect to your WordPress site. You can set a single background for the entire site or configure individual backgrounds for each post, page, or product.
Features:
<ul>
<li>Background image with smooth parallax scrolling effect</li>
<li>One image for all pages or individual backgrounds per page/post</li>
<li>Works vertically and horizontally</li>
<li>Various overlay patterns to choose from</li>
<li>Color overlay with opacity control</li>
<li>Boxed layout option with customizable margins</li>
<li>Mobile device detection with option to disable parallax on mobile</li>
<li>Compatible with WooCommerce products</li>
</ul>
Requirements:
<ul>
<li>Your theme must support the WordPress <a href="https://developer.wordpress.org/themes/functionality/custom-backgrounds/" rel="nofollow ugc">Custom Backgrounds</a> theme feature</li>
<li>For parallax effect, images should be at least 1920px x 1200px</li>
<li>PHP 8.0 or higher</li>
</ul>
<h3>Privacy Policy</h3>
This plugin does not collect, store, or transmit any personal data. All settings are stored locally in your WordPress database.

cbParallax

Custom background images with parallax effect for posts, pages and products.

Jellyfish backdrop vs cbParallax