This is a list of websites that may help in your research. I will add new ones as I find them. If you know of one not listed here, please let me know and I will add it.
Keep in mind that manuscripts are not just for people who make scrolls - they might contain a drawing of what you are looking for.
If any of these links don't work for you, try putting them in The Wayback Machine at archive.org
Google Translate will translate almost any language into almost any other. The results are not perfect, but they are good enough to see if you need to research a certain source further.
Locate a library that holds a book that you are interested in finding.
Internet Archive is a non-profit library of millions of free books, movies, software, music, and more. You may also be able to access web sites that have moved or may no longer be hosted.
Bibliotheque Nationale in France
The British Library Digitised Manuscripts
The British Library Catalogue of Illuminated Manuscripts
British Library Medieval Manuscript Blog
Codices Electronici Sangallenses - Medieval codices in the Abbe Library of St. Gallen
Digital Image Archive of Medieval Music
Digital Library Of The Commons Repository
A gateway to the international literature on the commons. The DLC provides free and open access to full-text articles, papers, and dissertations.
Digitized Medieval Manuscripts - DMMapp
e-codices - Virtual Manuscript Library of Switzerland
Online Sources for European History
Gugenberg Bible at Oxford’s Bodleian Library
Hathi Trust Digital Library
Internet Medieval Sourcebook - Fordham University
Special Treasures from the Library of The Jewish Theological Seminary
German museum images
The Labyrinth Resources for Medieval Studies sponsored by Georgetown University
Bibliotheque Municipale de Lyon
Medieval Illuminated Manuscripts
Medieval Manuscripts in Dutch Collections
The Morgan Library & Museum
Medieval & Renaissance manuscripts, books, music scores, drawings, prints, and more
The New York Public Library Digital Collections
The Online Medieval & Classical Library
Parker Library on the Web - manuscripts in the historic Parker Library at Corpus Christi College, Cambridge
Pages from the Past - A Legacy of Medieval Books in South Carolina Collections
Renascence Editions - An Online Repository of Works Printed in English Between the Years 1477 and 1799
St John's College Library Medieval Manuscript Image Index
The Schoyen Collection - manuscripts from around ht eworld spanning 3000 years of human culture & civilisation
The Vatican Library
Vatican Library Manuscripts
The Walters Art Museum Digitized Manuscripts
World Digital Library
York Archaeological Trust Media Library
The Book of Kells free to view online at The Library of Trinity College Dublin
Polonsky Foundation Digitization Project