Retina Images
This module provides an option for image styles to output high-resolution images, making them appear sharper on high-density displays like those on retina devices. When an image style with this option enabled is used, the module automatically serves higher resolution images to compatible devices.
Retina Images adds an option to all image effects included with core to allow them to output high resolution images for high DPI or retina displays. When enabled as part of an image style, this module returns high resolution images for all devices, as is recommended and explained in Thomas Fuchs' excellent blog post.
For best results you may need to specify a custom quality setting for each image style, which can be done easily with the Image Style Quality module.