Image from Xanten Gospels, a Carolingian manuscript from the 9th century, housed at the Royal Library of Belgium (Wikipedia page here); image from Wikipedia, assumed allowed under Fair Use.
Used in 2018-05-06 Update.
2788.13v
Image from Harley Golden Gospels, Harley MS 2788, a 9th century manuscript housed at the British Library; image assumed allowed under Fair Use.
Used in 2018-04-22 Update.
St. Riquier Gospels
Image from St. Riquier Gospels, a Carolingian manuscript from the 8th century, housed at the Bibliothèque Municipale d’Abbeville; image from Wikipedia, assumed allowed under Fair Use.
Used in 2018-04-08 Update.
Athelstan.2v
Image from Athelstan Psalter, a 9th century manuscript housed at the British Library; image assumed allowed under Fair Use.
Used in 2018-04-01 Update.
arihmetica 9
Image from De institutione arithmetica , a 9th-century manuscript housed at the Bamberg State Library (Wikipedia page here), citation link here, image assumed allowed under Fair Use.
Used in 2018-03-18 Update.
De bello Judaico – 5
Image from De bello Judaico, a 9th-century manuscript housed at the Bamberg State Library (Wikipedia page here), citation link here, image assumed allowed under Fair Use.
Used in 2018-03-04 Update.
Chludov Angel
Image from the Chludov Psalter, a 9th century manuscript in the Byzantine style; image from Wikimedia, assumed allowed under Fair Use.
Used in 2018-02-25 Update: Call With The Purely Functional Guy.
Clementine Screenshot
Image of Clementine from aTunes Screenshot
Image of aTunes from 
Aachen Gospels
Image from Aachen Gospels, a 9th Century Carolingian manuscript housed at the Aachen Cathedral. Image from Wikimedia, assumed allowed under Fair Use.
Used in 2014-11 Tweets.