WebP
Google's image format. Launched 2010. Lossy + lossless mode + alpha + animation. 25–35% smaller than JPEG at similar quality. Universal browser support since ~2020.
Built on the VP8 video codec (frame). Competitor for many years: JPEG XR (Microsoft, abandoned), JPEG XL (modern, better quality but Chrome dropped support 2022 → controversy). AVIF (2019) is the successor — better quality, even smaller files, but slower to encode. Modern best practice: serve AVIF with WebP fallback (via <picture>). cwebp + dwebp are CLI tools. Squoosh (Google) is a web-based converter.