English:
Creator: Dr. Hugh Welch Diamond (1808 - 1886)
Date: c. 1855
Format: Photograph; salt print from calotype negative
Material: Paper
Collection: The Royal Photographic Society Collection at the National Media Museum
Inventory no: 2003-5001/2/24914
Blog post: D is for Dr. Hugh Welch Diamond… Photography and the pseudoscience of physiognomy, National Media Museum

In May 1856 Dr. Hugh Welch Diamond, a physician at the Surrey County Asylum and Secretary to the Photographic Society of London, presented a paper to the Society called On the Application of Photography to the Physiognomy and Mental Phenomena of Insanity.
Diamond stated that photography was invaluable in the treatment of mental illness. He proposed that by studying the faces of patients, physicians could identify and diagnose mental complaints. These beliefs were rooted in the pseudoscience of physiognomy, where the face was seen as the mirror of the soul. For Diamond, the faces of the patients represented "types" of mental illness such as melancholia and delusional paranoia.

...the Photographer catches in a moment the permanent cloud, or the passing storm or sunshine of the soul and thus enables the Metaphysician to witness and trace out the visible and the invisible in one important branch of his researches into the Philosophy of the human mind...

Dr. H. W. Diamond, On the Application of Photography to the Physiognomy and Mental Phenomena of Insanity, The Photographic Journal, July, 1856.