Microforms are scaled-down reproductions of documents, typically either films or paper, made for the purposes of transmission, storage, reading, and printing. Microform images are commonly reduced to about 4% or of the original document size. For special purposes, greater optical reductions may be used.
Three formats are common: microfilm (reels), microfiche (flat sheets), and aperture cards. Microcards, also known as "micro-opaques", a format no longer produced, were similar to microfiche, but printed on cardboard rather than photographic film.
Using the daguerreotype process, John Benjamin Dancer was one of the first to produce microphotographs, in 1839.
He achieved a reduction ratio of 160:1. Dancer refined his reduction procedures with Frederick Scott Archer's wet collodion process, developed in 1850–51, but he dismissed his decades-long work on microphotographs as a personal hobby and did not document his procedures. The idea that microphotography could be no more than a novelty was an opinion shared in the 1858 Dictionary of Photography, which called the process "somewhat trifling and childish".
Microphotography was first suggested as a document preservation method in 1851 by the astronomer James Glaisher, and in 1853 by John Herschel, another astronomer. Both men attended the 1851 Great Exhibition in London, where the exhibit on photography greatly influenced Glaisher. He called it "the most remarkable discovery of modern times", and argued in his official report for using microphotography to preserve documents.
A pigeon post was in operation while Paris was besieged during the Franco-Prussian War of 1870–1871. The chemist Charles-Louis Barreswil proposed the application of photographic methods with prints of a reduced size. The prints were on photographic paper and did not exceed 40 mm, to permit insertion in a goose-quill or thin metal tube, which protected against the elements. The pigeons each carried a dispatch that was tightly rolled and tied with a thread, and then attached to a tail feather of the pigeon.