The LQIP approach, popularized by Medium, uses a very small placeholder image to enable a quicker initial page load. The idea is the placeholder gives the user a sense of the image shapes and color while consuming minimal bytes. The hires image then replaces the placeholder later in the page load cycle.

The approach may help with perceived performance, although in general more bytes will be consumed overall - the extra image, plus the JavaScript to make the placeholder work. This approach deserves more research and might remain plugin territory.

previously: adamsilverstein/modern-images-wp#19