Cnp balkans aircraft 01.jpg
Originally scanned from: GWS - The Great War: The Standard History of the All Europe Conflict (volume four) edited by H. W. Wilson and J. A. Hammerton (Amalgamated Press, London 1915)

According to http://www.firstworldwar.com/photos/sources.htm, “Each photo is believed to be copyright-expired except where indicated.” The site has been up for seven years and sources for the photos cited so it is reasonable this claim of copyright expired status has stood the test of time.

Note: other than the source of the image and the assertion of copyright free status, detail information such as credits for each photographer and image provider was not indicated for each image.
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Cnp balkans aircraft 01, A German aircraft over the Balkans., A German aircraft over the Balkans.
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Cnp balkans aircraft 01, Albatros C.III
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バルカン爆撃機 01型、バルカン半島を飛行中のドイツ軍機。バルカン半島を飛行中のドイツ軍機。
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バルカン爆撃機
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balkans balkan country balkan peninsula balkan wars asserted