Introduction
Responsive web design has solved many problems related to building websites that work across devices—fluid grids adapt our layouts, media queries adjust our styles, and flexible images scale to fit their containers. But there's one aspect of responsive design that remains frustratingly unsolved: the responsive images problem.
The issue is straightforward: responsive websites need images that adapt not just visually but also technically. When you set max-width: 100% on an image, it scales down beautifully on mobile devices, but there's a hidden problem—that mobile device still downloaded the full-size desktop image. A user on a smartphone with a 320-pixel-wide screen doesn't need your 1200-pixel-wide hero image, yet they're downloading it anyway, wasting bandwidth and slowing down page load times.