A specialised XML sitemap that lists image URLs, allowing search engines to discover images they might miss from HTML alone — particularly useful for image-heavy galleries, lazy-loaded grids, and images served via JavaScript. Either a standalone file or extension namespace within a regular sitemap (
xmlns:image="http://www.google.com/schemas/sitemap-image/1.1"). Each image entry can include <image:loc>, <image:caption>, and <image:title>. Google has reduced reliance on image sitemaps as its image discovery has improved, but they remain a no-cost win for sites where images are core to the value proposition.