This is a file from the Wikimedia Commons. The description on its description page there is shown below.
Description
Deutsch:Flagge des Herzogtums Braunschweig; Verhältnis (2:3) Image File history File links Commons-logo. ...
English:Flag of the duchy of Brunswick; Ratio (2:3)
Source
Own Work
Date
09.06.2006
Author
David Liuzzo
Permission
This image is a national, governmental, military, royal/vice-regal or historical flag. The flag may have been contributed by a user or taken and/or modified from the Central Intelligence Agency's World Factbook. Many have also been color-modified based on data from the World Flag Database. Such flags are ineligible for copyright but they are protected by Article 6' of the Paris Convention (Protection of State Emblems, and Names, Abbreviations and Emblems of International Intergovernmental Organizations). Representations of national flags are subject to copyright as original works of art and do not fall under Bridgeman Art Library Ltd. v. Corel Corporation's purview as they are not representations of two-dimensional works of art.
Note to contributors: Use of this tag to indicate copyright status is deprecated, please use one of the other Commons:Copyright tags for this purpose. For images from the CIA's World Factbook, use {{PD-USGov-CIA-WF}}.
File links
The following pages on the English Wikipedia link to this file (pages on other projects are not listed):
This is a gallery of bicolor flags having fields split horizontally, vertically, or diagonally into differently colored sub-fields. ... This is a gallery of pairs (or larger groupings) of flags that exhibit such similarity in design that they can be difficult to distinguish. ...