Why it matters
AVIF and WebP are typically 25-50% smaller than JPEG/PNG at the same quality and are supported by every current browser.
How to fix it
Serve AVIF or WebP (content negotiation, <picture>, or next/image). Keep SVG for vector art.
Example
<picture><source srcset="/hero.avif" type="image/avif"><img src="/hero.jpg" alt="…"></picture>More performance rules
void perf reports 25 rules in this category. Core Web Vitals and bytes: LCP, CLS, TBT, TTFB, JavaScript, CSS, fonts, images, caching and compression, measured as the median of several runs on a throttled mobile and a desktop profile.
lcp-image-lazyLCP image is lazy-loadedlcp-image-no-priorityLCP image has no fetchpriority="high"lcp-background-imageLCP element is a CSS background imageimage-oversizedImage is much larger than its rendered sizeimages-missing-dimensionsImages without width/height or aspect-ratiorender-blockingRender-blocking resources delay first paintno-text-compressionText resources are served uncompressedcache-headersHashed static assets are not cached long-term