Who is the most ancient mathematician of which we have a photograph? 
(or, in the same vein, what is the oldest photograph of a mathematician) 
A quick search on MacTutor History of Mathematics gives Binet (b.1786) as a pretender with Cauchy (b.1789) coming close...



Oldest photographed mathematician
Most ancient: Wikipedia has a [daguerreotype of Gauss](https://en.wikipedia.org/wiki/Carl_Friedrich_Gauss) (1777–1855) on his deathbed. Or possibly [Farkas Bolyai](https://archive.org/stream/jstor-2968693#page/n2) (1775–1856) in what look like similar circumstances.


Less ancient, but allegedly photographed earlier: Googling "daguerreotype mathematician" gives


• c. [1840](https://www.gettyimages.com/license/50799253), [1840](https://www.gettyimages.com/license/50799251): Augustus De Morgan (1806–1871)  

• c. [1842–1843](http://www.claymath.org/publications/ada-lovelaces-mathematical-papers): Ada Lovelace (1815–1852)  

• c. [1843](https://commons.wikimedia.org/wiki/File:Friedrich_Wilhelm_Bessel_1843_B.jpg): Friedrich Wilhelm Bessel (1784–1846)  

• c. [1843](http://www.mhsgent.ugent.be/engl-plat12.html): Joseph Plateau (1801–1883)  

• c. [1843](https://www.gettyimages.com/license/90732052), [1847–1851](https://en.wikipedia.org/wiki/File:Charles_Babbage_by_Antoine_Claudet_c1847-51-crop.jpg): Charles Babbage (1791–1871)  

• c. [1844](https://commons.wikimedia.org/wiki/File:W_H_F_Talbot.jpg): William Henry Fox Talbot (1800–1877)  

• c. [1845](https://www.gettyimages.com/license/90772948): François Arago (1786–1853)  

• c. [1845](http://www-history.mcs.st-and.ac.uk/BigPictures/Hamilton_2.jpeg): William Rowan Hamilton (1805–1865) (per [frontispiece](//zbmath.org/?q=an:57.0034.09))  

• c. [1846](//en.wikisource.org/wiki/Page:Popular_Science_Monthly_Volume_72.djvu/191): William Thomson (1824–1907)  

• c. [1846](https://www.gettyimages.com/license/463906191): John Couch Adams (1819–1892)  

• c. [1847](https://www.gettyimages.com/license/2641935): Hermann von Helmholtz (1821–1894)  

• c. [1848](https://www.npg.org.uk/collections/search/portrait/mw09661/Sir-John-Frederick-William-Herschel-1st-Bt): John Herschel (1792–1871).


