This plugin allows you to add and image as background of posts, pages or custom post type in general (in the same way as a thumbnail).
<ul>
<li>This is a rewrite of my old plugin <a href="https://wordpress.org/plugins/post-background/" rel="ugc">Post Background</a> which I do not have access anymore. *</li>
</ul>

WP Post Background

This plugin allows you to add and image as background of posts, pages or custom post type in general (in the same way as a thumbnail).

Ryan Novotny

Add the particles.js JavaScript library to add cool particle effects to any WordPress page ( demo: <a href="https://particlebackground.com/" rel="nofollow ugc">https://particlebackground.com/</a> ).
Uses shortcode or easy options for adding to the front page or blog page of WordPress.
Fully customize the particles using your own JSON or the built in color & density settings
Leave a comment in the support forum for any suggestions or bugs.
<h4>Features</h4>
Add particle background to home or blog pages with one click 
Add particle background to any page using shortcodes 
Customize the background color and dot color 
Add any HTML just like a WordPress post to display on top of the particle background (optional)

Particle Background WP

Particle Backgrounds WP lets you easily add cool particle-style backgrounds to any page.

WP Post Background vs Particle Background WP