By the end of 2013, the average web page served 1,030Kb of images, much to the chagrin of low bandwidth and pay-per-kilobyte users. The need to serve smaller images where appropriate, and to be able to control the scale and crop of images at all sizes, is imperative to creating a light weight and editorially rich web experiences. This is where responsive images come in. Unfortunately, we don't have a standard solution yet, and of those proposed, images will be swapped based on viewport information, not element information. Until we have a standard solution, you've got to pick your favorite hack. In order to use borealis, you need to both include borealis.js on your site and set up the data-borealis-srcs attribute on your desired image. data-borealis-srcs needs to be written in key: value pairs separated by a comma ,, with the key being the min-width pixel width when you would like to swap out an image and the value being the URL to the image. The first item in data-borealis-srcs should not have a key and will be the default. In order to prevent extra image requests, do not include the src attribute in the image definition.