The website you linked to uses the background-image trick: instead of resizing the image, it uses an image as the background of a div instead, then it applies the appropriate styles to the div:
height: 840px;
background-image: url('pathToImage');
background-size: cover;
background-position: center center;
This is achieved using CSS only - no need for Angular or even JavaScript.
WURFL Image Tailor does something different - it actually serves a different sized image (image size and file size) based on screen width. This is useful when you don't want browsers on smaller screens to download images in their original resolution and size. (The assumption is that smaller screens mean mobile and mobile means slower connections.)