What do I need to do for responsive images out of the box?
Modules
https://www.drupal.org/project/easy_responsive_images
https://www.drupal.org/project/image_style_generate
https://www.drupal.org/project/image_styles_builder
Drupal CMS
Copy image styles from Drupal CMS.
Drimage
https://www.drupal.org/project/drimage
Easy setup, combined with views responsive grid.
Notes
https://www.drupal.org/docs/contributed-modules/image-optimize/site-builders-guide
Project