Benson, P., & Perrett, D. (1991). Computer averaging and manipulations of faces. In P. Wombell (ed.), Photovideo: Photography in the age of the computer (pp. 32–38). London: Rivers Oram Press.
galton.org
Galton, F. (1878). Composite portraits.Journal of the Anthropological Institute of Great Britain and Ireland, 8, 132–142.