Serving sharp images to high density screens - JakeArchibald.com
If you want your images to be as sharp as possible, you need to target images at the user's device pixels, rather than their CSS pixels.
Responsive Images the Simple Way
The responsive images spec is fantastic and covers a lot of use cases, but in my experience, most of the time you’ll only need to understand one of them: Serving a different sized copy of the same image depending on the user’s viewport width.
What if we got aspect-ratio sized images by doing almost nothing? | CSS-Tricks
Time-saving CSS techniques to create responsive images
Images in a responsive web
Coding for Retina on the web
Goodbye -9999px: A New CSS Image Replacement Technique
Control image aspect ratios with CSS3
3+ Ways to Preload Images Using CSS, JavaScript, or Ajax • Perishable Press
Responsive HTML images
Giving "Responsive HTML images" a go