Leon Battista Alberti —
Photo Credit: Di G. Benaglia - Pubblico dominio, https://commons.wikimedia.org/w/index.php?curid=15884503

The Alberti Cipher disk —
Photo Credit: By Augusto Buonafalce - De componendis cifris, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=3733873

Anti-pope Clement VII — Modern portrait by Calixte Serrur
Photo Credit: By Henri Auguste César Serrur - Les papes en Avignon, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=17864496

Isḥāq al-Kindī (801-873 CE) —
Photo Credit:

First page of On Deciphering Cryptographic Messages — The first page of al-Kindi's manuscript On Deciphering Cryptographic Messages, containing the oldest known description of cryptanalysis by frequency analysis.
Photo Credit: Public Domain, https://commons.wikimedia.org/w/index.php?curid=34672454

statue of Al-Khalil ibn Ahmad al-Farahidi in Basra —
Photo Credit: By احمد محمود خضير - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=27778602

Caesar cipher diagram — The action of a Caesar cipher is to replace each plaintext letter with a different one a fixed number of places down the alphabet. The cipher illustrated here uses a left shift of three, so that (for example) each occurrence of E in the plaintext becomes B in the ciphertext.
Photo Credit: Public Domain, https://commons.wikimedia.org/w/index.php?curid=30693472

Suetonius, De vita Caesarum — Berlin State Library (Ms. lat. fol. 28, fol. 73v.)
Photo Credit: By Suetonius - 2d copy, Public Domain, https://commons.wikimedia.org/w/index.php?curid=48540156

Suetonius from the 15th-century Nuremberg Chronicle —
Photo Credit: Public Domain, https://commons.wikimedia.org/w/index.php?curid=1686407

Caesar cipher mechanism — A construction of two rotating disks with a Caesar cipher can be used to encrypt or decrypt the code
Photo Credit: By Hubert Berberich (HubiB) - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=25964875

Merkle Puzzles —
Photo Credit: (c) 2020 ShaneBow