The `Link` header exists which is the moral equivalent of the `link` element in HTML. That way you can express link relations on resources whose representations do not have hyperlinks. Example:

    HTTP/1.1 200 OK
    Content-Length: 153054
    Content-Type: image/webp
    Link: <http://example.com/mediterranian-2019/olives.webp>;
      rel="next"; title="next image in album"

See https://tools.ietf.org/html/rfc8288