You live in the midst of deception;
in their deceit they refuse to acknowledge me,
declares the LORD.
Jeremiah 9:6
"Darwin’s book on facial expressions, titled The Expression of the Emotions in Man and Animals, was his third major work on his evolutionary theory. Originally intended to be a single chapter in The Descent of Man, Darwin
added so much material that it was 
eventually published separately in
1872. A best seller when published, out-selling Darwin’s other books, it
has never been out of print since then.
The year 2022 is the 150th anniversary of the Expression book, often described as Darwin’s “forgotten masterpiece.”
Although Darwin admitted that some of the photographs he used were
posed, and others were modified, Paul Ekman (social psychologist at the
University of California, San Francisco) “found from the Darwin archives
and correspondence that the alterations were more extensive” than
previously believed.
Instead of photographing natural expressions elicited by typical humans
responding to real situations, many of the photographs, it was implied
or openly stated, were actually posed. Darwin went far beyond simply
retouching the photographs, which would have been a problem even if
Darwin had admitted that the photographs were doctored. The only
photograph in the Expressions book that we know for sure was not posed was that of Darwin’s dog Polly.
Darwin used several photographs taken by London photographer Oscar
Rejlander because he “proved especially skillful at securing the
expressions Darwin wanted.”
Rejlander is most often identified with the “composite printing”
technique today called “trick photography” in which several photographic
negatives were artfully combined to create a photographic print made
from several pictures.
As a result, Rejlander was able to manipulate his
images, and produce convincing photorealistic images that were
artificially assembled in the darkroom.
Rejlander even occasionally used himself at the subject for his
photographs. Trodger determined that one picture of Rejlander’s wife was
specifically posed for Darwin to illustrate “a most convincing sneer.”
Rejlander put his trick photography skills to good use to help Darwin
“prove” his thesis. The first, and most celebrated photograph in
Darwin’s Expression book, is of a weeping baby that turned out
to be a photographic copy of a drawing made from an original photograph
that Rejlander altered.
Rejlander’s skills enabled him to effectively “highlight elements of
the image Darwin sought to express” such as in one photograph where the
“child’s hair, cheeks, and brow … seem slightly more lively and
energetic in the drawn version.”
Another manipulation was to put the child into an unnaturally small
chair by means of trick photography, making the child look
“larger-than-life.” The goal was to artificially create an “illustration
that would have seemed persuasive to Darwin’s readers.”
Darwin also used eight photographs by the famous Paris physiologist
Guillaume-Benjamin-Amand Duchenne who used electrodes to stimulate the
facial muscles in mental patients and then take their photograph.
He is also credited with the discovery of Duchenne muscular dystrophy
which was named after him. Duchenne published a book that contained
photographs of patients forced to endure these barbaric treatments.
From another set of more than 40 photographs of mental patients, Darwin
selected a woman diagnosed as insane to use as an example of a “normal”
human expression.
Beth Mole noted that “Darwin’s experiment included only 20 or so
participants—mostly his friends and family—and he ignored some of the
data.”
The major issue Darwin avoided is the unbridgeable gap that exists
between humans and animals. Only humans have the face muscles required
to express the emotions that Darwin was looking for in animals. Humans
have on average 43 facial muscles and chimps, supposedly our closest
relatives, have only 23." CEH