An image sitemap is a specialized XML sitemap, or an extension added to an existing page sitemap, that explicitly lists the images on each URL rather than leaving crawlers to discover them purely by parsing page HTML. It gives search engines a direct, structured signal about which images exist and where.
It matters most for sites where images are loaded dynamically through JavaScript, embedded as CSS backgrounds, or otherwise harder for a crawler to find through normal HTML parsing, cases where an image sitemap can surface visual content that would otherwise be missed or discovered much later. For a straightforward site with images sitting in plain <img> tags, a dedicated image sitemap adds less value, since crawlers generally find those without help. It's a relatively low-effort addition either way, and for any site relying on Google Images as a meaningful traffic source, it's worth having as one more way to make sure images actually get seen.
