This plugin creates the image files required by the Retina (or any high-DPI) devices and displays them to your visitors accordingly. Your website will look beautiful and sharp on every device. The retina images will be generated for you automatically (you can also do it manually) and served to the visitors. You will be able to control everything from a nice dashboard.
It supports 4 different methods to serve the images to your visitors:
Pick the one that works best with your hosting and environment. WordPress Multi-site are supported as well. WP Retina 2x also loves WPEngine and strongly recommend it for your hosting. I am trying to keep a tutorial about this plugin up to date and comprehensive here.