According to a commonly used definition, vernacular photography is ordinary, banal, trivial—that is to say, related to everyday life. Certainly many vernacular images, such as those taken by amateurs, are so. But a number of images—post-mortem photos, medical images, photographs of road accidents, for example—show much more of the uncommon. This definition of the vernacular as ordinary seems too limited. Vernacular photography is a much broader whole that must be able to encompass images by amateurs and those taken by scientists, the police, insurance agents, studio operators, and automatic cameras, but also press photos; fashion, wedding, or identification photographs; X-rays; photographic objects; and many other examples of the medium’s numerous applications. Vernacular photography, like the vernacular in general, is that which is either utilitarian, domestic, or popular, or sometimes two of those aspects, or even all three together. (Chéroux)
Chéroux Clément and Shane B Lillis. Since 1839… : Eleven Essays on Photography. RIC Books Ryerson Image Center ; The MIT Press 2021.