Image from Wikimedia Commons
Photographer unidentified - Public Domain
unknown - Public Domain
The Notman Studio - Public Domain
Guido van Nispen - CC BY 2.0
Wilhelm Fechner (1835-1909) [http://www.fotorevers.eu/katalog1.php?details=2522] - Public Domain
Dipz99 - CC BY-SA 3.0
Public Domain
Chemical and Metallurgical Engineering, Volume 27, 1922 - Public Domain
Félix, Paris - Public Domain
original uploader - Public Domain
Ford Motor Company (Allen's radio sponsor). Ford used its advertising agency, J. Walter Thompson, to distribute this publicity material. - Public Domain
Harper & Brothers - Public Domain
Bdavis1531 - CC BY-SA 3.0
StagiaireMGIMO - CC BY-SA 3.0
Rcarlberg - CC BY-SA 3.0
Unattributed - Public Domain
Tina Modotti - Public Domain
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Morselli, Enrico Agostino, 1852-1929
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Mujibur Rahman, Sheikh, 1920-1975
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Photographer unidentified - Public Domain
Holmes, Mary Jane, 1825-1907
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Nolan, Sidney, 1917-1992
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unknown - Public Domain
Togan, Ahmed Zeki Velidi, 1890-1970
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The Notman Studio - Public Domain
Warren, William, 1812-1888
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Guido van Nispen - CC BY 2.0
Keyzer, Carl de, 1958-
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Tillyard, R. J. (Robin John), 1881-
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Leray, Jean, 1906-1998
Image from Wikimedia Commons
Wilhelm Fechner (1835-1909) [http://www.fotorevers.eu/katalog1.php?details=2522] - Public Domain
Baginsky, A. (Adolf), 1843-1918
Image from Wikimedia Commons
Dipz99 - CC BY-SA 3.0
Correa, Charles, 1930-....
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Public Domain
Ward, Henry A. (Henry Augustus), 1834-1906
Image from Wikimedia Commons
Chemical and Metallurgical Engineering, Volume 27, 1922 - Public Domain
Capen, Samuel Paul, 1878-1956
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Félix, Paris - Public Domain
Sully, Mariette
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original uploader - Public Domain
Uz, Johann Peter, 1720-1796
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Rarick, John R., 1924-2009
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Ford Motor Company (Allen's radio sponsor). Ford used its advertising agency, J. Walter Thompson, to distribute this publicity material. - Public Domain
Wilson, Earl, 1907-1987
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Harper & Brothers - Public Domain
Borden, Matthew C. D. (Matthew Chaloner Durfee), 1842-1912
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Hamilton, Lillias, 1858-1925
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Francis, Kay, 1905-1968
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Bdavis1531 - CC BY-SA 3.0
Snelling, Richard Arkwright, 1927-1991
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StagiaireMGIMO - CC BY-SA 3.0
Fassbaender, Brigitte
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Farnum, William, 1876-1953
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Grafton, Charles Fitzroy, Duke of, 1683-1757
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Rcarlberg - CC BY-SA 3.0
Sherman, Jeffrey C.
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Reagon, Bernice Johnson, 1942-
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Ranger, Henry Ward, 1858-1916
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Unattributed - Public Domain
Rosenhain, Jakob, 1813-1894
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Tina Modotti - Public Domain
Rodríguez Lozano, Manuel, 1895-1971
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unknown - Public Domain
Ardouin, B. (Beaubrun), 1796-1865