eleventy-img is a utility for Eleventy static site generator users that performs build-time image transformations, supporting both vector and raster images. It allows developers to output multiple sizes and formats, cache remote images locally, and maintain full control over HTML markup with `<picture>`, `<img>`, or CSS `background-image` elements. The tool is ideal for developers looking to optimize images for performance while preserving responsive design and accessibility features like `width` and `height` attributes.