Selected images of manuscripts are placed online usually because the manuscripts are too damaged to be handled very much without expert care, or because the department putting up the manuscript was not funded well enough to place the entire manuscript on the internet. Such is the case in some of the following manuscripts.
As you can see, though, placing only part of a manuscript online does not necessarily take away from the overall presentation. For some online presentations, the audience is made up of the general public, schoolchildren, or scholars that are more interested in the subject of the piece rather than the piece itself.
The Ellesmere Chaucer Facsimile
Long Island University has placed miniatures of the pilgrims of Chaucer’s Canterbury Tales online in this page. Though there are actually 31 pilgrims (or 29, depending on your research), there are only 23 portraits here: the ones missing are the tradesmen. If you click on a single image until it takes you to a high-resolution version of the image.
Byzantine Medieval Hypertexts
This web site was produced by a doctoral student at the Univ. of Texas at Austin, working with images produced by faculty at Univ. Notre Dame. The text used here is the Theodore Psalter.
Treasures from the UK National Archives
This site provides selections from a number of manuscripts, including a copy of the Magna Carta, the Domesday Book, the Treaty of Calais, and others. The images are not high-resolution or annotated for professional use but described for the general public. Options on this website include viewing a transcript, sending as an e-card, and bookmarking the site with Facebook, Reddit, or Yahoo--definitely for the general public!
Gaston Phoebus, “Book of the Hunt”
This hunting manual has been cropped and scanned only for its miniatures. However, the miniatures can be enlarged to a fairly good resolution image. This manuscript has been placed online by the Bibliothéque National de France.