'Images and documents' is a cover term for a wide variety of formats of material held by the Mills Archive, including:
These items together form the 'Archive' proper, one of two sets of material held by the Mills Archive alongside the Library. Although they come in many forms, they have certain things in common which distinguish them from library items:
Uniqueness: By and large, these items are unique, unlike books or journals which are printed in many copies.
Circumstances of creation: These items tend to have been created for particular purposes at particular times, and were only intended for the use of specific people (e.g. a letter is only intended to be read by the person it is addressed to). Books on the other hand are intended for a general audience. This can make 'archival' items harder to understand.
Relationship to other items: These items tend not to stand alone, like books, but are usually part of a larger collection. The catalogue allows items to be seen in the context of these larger collections of which they form a part.