Phillip.Gooch

Backdrop is a site background customizer with power greater than the mere stock background selector included with WordPress. What can backdrop do that the default can’t? I’m glad you asked…
<ul>
<li>More than just boring backgrounds, flexible backgrounds, parallax backgrounds, even sliding backgrounds are stuffed in here too (don’t worry, the boring ones are still around as well).</li>
<li>Options, options, options! More options that you can shake a well sharpened stick at.</li>
<li>Uses the WordPress customizer interface so you can see your changes as you make them.</li>
<li>One click HiDpi (or retina) backgrounds, make it look all purdy on that fancy screen.</li>
<li>Theme schmeme, we don’t need support in your stinkin theme, backdrop can force it’s way into nearly any theme.</li>
<li>Calls external JS and CSS files that are appropriately cached.</li>
<li>Advanced options for those in the know with CSS.</li>
<li>Built for the smoothest animations possible.</li>
</ul>
Note: Starting with version 2.0 Backdrop will no longer work it’s magic with older versions of Internet Explorer (before version 10). If you want to support animations on older versions of IE then please use Backdrop 1.X.
Note: Your Backdrop settings will not be transfered from 1.X to 2.X, you will need to re-set your backdrop on update.

Backdrop

Backdrop is an improved site background customizer allowing for all manner of fancy things.

ishitaka

XO Post Background is a plugin to set background image and color for each post.
Background image details (size, position, etc.) and background color can only be set in WordPress 5.7 or higher block editors.

XO Post Background

XO Post Background is a plugin to set background image and color for each post.

Backdrop vs XO Post Background