More than 1,600 ancient manuscripts from the renowned Eastern Orthodox Monastery of St. Catherine’s on Mt. Sinai have been made available online! The images, digitized from older microfilms, are of very good quality. Here is one such image of Greek Manuscript 212, a ninth century Greek lectionary "miniature codex" classified in the Gregory-Aland system as l 846:
There is an option to download really high-res files, including TIFF files, but that option was not working for me. Perhaps they will make that available in the near future.
To quote from the catalogue website, the monastery "is home to reputedly the oldest continuously run library in existence today. Its holdings of religious and secular manuscripts are legendary and allegedly second only in number to the collection held by the Vatican: from bibles, to patristic works, to liturgies and prayers books, and on to legal documents such as deeds, court cases, Fatwahs (legal opinions). The greater proportion of the manuscripts were copied in Greek, and then in Syriac, Georgian, Coptic, Armenian, Arabic, Ottoman Turkish, and Ethiopic, as well as Old Church Slavonic."
The new site also includes a digitized copy of Kenneth W. Clark's famous Checklist of Manuscripts in St. Catherine’s Monastery, Mount Sinai Microfilmed for the Library of Congress (1950).