To quote
https://wiki.creativecommons.org/wiki/Marking_Works_Technical
Included Objects
Objects included in web pages, such as images, should be annotated as above within their
"host" web pages. Ideally all included objects should also embed object format
native notice and metadata as described below, but this is only crucial for objects where
the publisher intends for or is concerned about distribution outside the context of the
"host" web page.
Metadata about include objects that have their own URIs should be qualified with about,
as rel="license" without an about attribute makes a statement about the current
document (which is the "host" web page). Example:
Photo licensed under <a
about="http://example.com/some-image.png"
rel="license"
href="https://creativecommons.org/licenses/by/4.0/">cc by 4.0</a>.
Perhaps this could be added to Commons as a mediawiki extension for Google to start
picking it up and showing the licensing information in its search results. Currently
Commons shows link tags with rel="license" attribute but they specify the whole
page license, like they should.
-- Sveta