Justin Tadlock

A plugin for allowing users to set a custom background on a per-post basis. This plugin hooks into the WordPress <code>custom-background</code> theme feature and overwrites the values on single post views if the post has been given a custom background.
<h3>Features</h3>
This plugin creates a custom meta box on the edit post screen. From that point, you can select a custom color and/or image. If you select an image, you’ll be presented with additional options for how the image appears on the site.
<h3>Requirements</h3>
Your theme must support the core WordPress implementation of the <a href="https://codex.wordpress.org/Custom_Backgrounds" rel="nofollow ugc">Custom Backgrounds</a> theme feature.

Custom Background Extended

Allows users to create a custom background on a per-post basis.

Alexandru Vornicescu

This is a WordPress plugin.
If you want to resize images in your posts automatically so the page will load faster and use less bandwidth then this plugin can help you.
To take effect just open a post or page and all images in that post will be resized to a smaller version.
It will replace the URLs of the images that are too big with URLs of the resized images that will fit into the posts.
The plugin will keep the original copy of all image files.
Note: With version 4.3 now you can resize images in Text Widgets.
Note: The filter – “wp_make_content_images_responsive” will be deactivated because with this plugin we will not need anymore.

Resize Images In Posts

This plugin will resize images in your posts.

Custom Background Extended vs Resize Images In Posts