Why it matters
Images start at low priority until layout proves they are in the viewport. fetchpriority="high" lets the LCP image download immediately, often saving 0.5-1 s.
How to fix it
Add fetchpriority="high" to the LCP <img> (Next 16: fetchPriority="high" or preload on <Image>). Use it on at most one image per page.
Example
<img src="/hero.avif" fetchpriority="high" alt="…">References
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.
too-many-fontsToo many font files are downloadedimage-budgetImage transfer exceeds the budgettoo-many-requestsPage makes many requestslcp-image-lazyLCP image is lazy-loadedlcp-background-imageLCP element is a CSS background imageimage-oversizedImage is much larger than its rendered sizeimage-legacy-formatImage served in a legacy formatimages-missing-dimensionsImages without width/height or aspect-ratio