Responsive images for RL occur within the following breakpoints:

Desktop - 992 +
Tablet portrait - 768 - 991
Phone landscape - 480 - 767
Phone portrait - up to 479

Scalable Images are used when it is necessary to have the hero or other image scale within the parent container.

This would be for when the developer needs an image to be flexible enough to be manipulated within the container due to limitations of the composition or other factors, or if someone just wants to see it scale down. 

How to use scalable images: