Background Image Cropper
This plugin is a WordPress core feature-plugin that adds cropping to background images for parity with header images. For this particular feature the implementation is quite simple, but it’s starting out as a plugin to gauge user interest in this feature and whether the feature improves the user experience of background images.
This plugin requires WordPress 4.3 Beta 3 or later.
If you’re interested in contributing to this project, ping @celloexpressions on WordPress core Slack. Please comment on the trac ticket with ideas and feedback: https://core.trac.wordpress.org/ticket/32403.
Take the easy route and install through the WordPress plugin installer OR
Click to Download the .zip file and upload the unzipped folder to the
Activate the plugin through the ‘Plugins’ menu in WordPress
Visit the Customizer (Appearance -> Customize) to change your background image and be able to crop it after selecting it.