A sitemap or sitemap extension providing information that helps search engines discover images.
An image sitemap provides search engines with information about images associated with website pages. It can be a separate sitemap or image information added to an existing one. Its purpose is discovery: identifying image resources that might otherwise be harder for a crawler to find.
The sitemap does not replace the image itself, the page containing it or a useful text alternative where one is needed. Listing an inaccessible image URL will not make the resource accessible. Nor does a sitemap guarantee that an image will be indexed or selected for a particular search appearance. It is one part of making the intended content discoverable.
Maintenance should follow the actual media inventory. If an image moves to a new delivery location or is removed from a page, the sitemap should not continue advertising a stale association indefinitely. A plugin may generate entries automatically, but that does not establish that the entries match the current public site.
Takeaway: Use image sitemap information to support discovery, then verify the listed files and their page context. Keep it synchronized with real media rather than treating submission as a visibility guarantee.
Example
A landscape designer publishes project galleries whose images are loaded by a custom component. The team checks which image URLs are discoverable and includes appropriate image entries in its sitemap. It also verifies that the actual photographs load publicly and that each project page explains what the images show.
What to check
Inspect a sample of sitemap entries after changing a media plugin or delivery domain. Open both the containing page and the image resource. Check access restrictions and stale URLs before submitting the sitemap again; repeated submission cannot repair a broken file path.
For more detail, see Google image sitemap documentation.