Drawing an image takes a fraction of a second, so each one is kept in files/og-images/<kind>/ after it is first asked for, and served from there.
When images are drawn again
- When the record changes: saving an item, collection, file, exhibit, exhibit page or simple page deletes its cached image. Saving a file or an item also refreshes the item's and its collection's images, which may show it.
- When the template changes: saving a template, or choosing another default, deletes the cached images of its kind.
- When an image is older than Keep cached images (7 days by default).
Each page's image address carries a version (?v=…) that changes with the record and the template, so networks that keep their own copy fetch the new image.
Deleting every cached image
Delete cached images on the OG Images page empties the cache, for example after changing the site's title or the theme's logo, which every image may show. The panel shows how many images are cached and their size.