Mashable.com is one of the most popular social media and technology news site. It uses WordPress as its CMS and implements best technologies available to make the site better and faster.
One of the things that it implements is lazy loading of images. The images fade in, that is, get loaded only when you scroll past them. This improves page speed and also saves bandwidth.
But its not very difficult to implement mashable style dynamic image loading. In fact, its a matter of installing the lazy load WordPress plugin. The plugin works automatically for all the images on your website, including the gravatars in comments.
In case you are not using WordPress and you still want to implement lazy loading of images on your website, you need to implemet the JQuery lazyloading on your website.