There has been so many requests regarding "live computation" during node add/edit. Here's how i got mine working without breaking anything. This link pointed me to the right direction.

Create a custom module. Change all instances of MYMODULE to the name of your module

Table of Content #

• General Requirements
• Specific Requirements
• Steps
• F.A.Q.

General Requirements #

Add an interface to upload multiple background images to be changed with a set interval.

https://www.drupal.org/project/bg_rotate

Add an interface to upload multiple background images to be changed with a set interval.

https://www.drupal.org/project/bg_rotate

The cover image format resizes an image down (or optionally up) to the smallest
size that completely covers the specified height and width while maintaining
ratio.

https://www.drupal.org/project/image_format_cover

It works exactly like Client-side adaptive image, but print div tag with image un background style which can be more easy to integrate in some specific design cases.

https://www.drupal.org/project/cs_adaptive_background_image