This is a file from the Wikimedia Commons. The description on its description page there is shown below.
The flag of Jersey. It is from the xrmap flag collection, specifically "uk_jersey.svg" in flags-2.6-src.tar.bz2. The README file in that collection says of the SVG flags "We release them in the public domain". Image File history File links Commons-logo. ...
This file has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. This applies worldwide.
The Channel Islands are a group of islands off the coast of Normandy, France, in the English Channel. ... This is a list of the countries of the world by continent with their national flags and capitals. ... Flag of Alderney Alderney is also a suburb of Poole in Dorset, England Alderney (French Aurigny, Auregnais Aoeurgny) is the most northerly of the Channel Islands and a British crown dependency. ... Flag ratio: 3:5 The flag of Jersey was adopted by the States of Jersey on June 12, 1979, proclaimed by the Queen on December 10, 1980 and first officially hoisted on April 1, 1981. ... Members of the International Cricket Council. ...