The VMS is an illustrated manuscript handwritten in an unknown writing system

[Anton]

I believe that if everyone basically agrees that these portions of the MS are images (and not e.g. blots or something), then a separate statement (or several ones) can be devoted to specifying what kind of images are those (that would fit into the Images section, while this one is just introductory Generic).

For this generic statement we need just to pick a general word most fitting.