Spinoza —
Photo Credit: By anonymous, Public Domain, https://commons.wikimedia.org/w/index.php?curid=303545

The Works of Jacob Behmen — 18th-century illustration by Dionysius Andreas Freher for the book
Photo Credit: Public Domain, https://commons.wikimedia.org/w/index.php?curid=57449504

Jakob Böhme — anonymous portrait
Photo Credit: Public Domain, https://commons.wikimedia.org/w/index.php?curid=663301

The first volume of Das Kapital —
Photo Credit: Public Domain, https://commons.wikimedia.org/w/index.php?curid=33666954

Only surviving page from the first draft of the Manifesto, handwritten by Karl Marx —
Photo Credit: https://en.wikipedia.org/wiki/The_Communist_Manifesto#/media/File:Iishmarx.jpg

Friedrich Engels: Die Lage der arbeitenden Klasse in England —
Photo Credit: Public Domain, https://commons.wikimedia.org/w/index.php?curid=37252856

Friedrich Engels in 1868 —
Photo Credit: By George Lester, Manchester photographer - Public Domain, https://commons.wikimedia.org/w/index.php?curid=1195844

Marx, Engels, and Marx' daughters — Karl Marx (1818–1883), Friedrich Engels (1820–1895), and Marx's daughters: Jenny Caroline (1844–1883), Jenny Julia Eleanor (1855–1898), and Jenny Laura (1845–1911). Photograph c. 1864.
Photo Credit: Public Domain, https://commons.wikimedia.org/w/index.php?curid=1417144

Jenny von Westphalen in the 1830s —
Photo Credit: Public Domain, https://commons.wikimedia.org/w/index.php?curid=107371886

The Electoral Palace, the main building of the University of Bonn —
Photo Credit: By I, Der Wolf im Wald, CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=2462942

seal of the University of Bonn —
Photo Credit: Public Domain, https://commons.wikimedia.org/w/index.php?curid=65121673