Dating of photograph
It's probably due to the fact that until about 1885 or 1900 at the latest, photography was not affordable to the masses and the processing could be complex.
Therefore, the industry was very much controlled by professional photographers and that meant that getting one's photograph taken was a formal event.
By 1871, the gelatin dry plate method made exposure times short enough that cameras could be hand held (ie, fraction of a second).
By 1878, technology shortened exposure times to a fraction of a second, about 1/25th of a second.
Of course, it's reasonable to assume that not all photographers had the most advanced equipment the moment it became available.
Guys hoping to get noticed on online dating sites should take off their shirts, at least those with six-pack abs, according to new survey results by one online matchmaker that also provide advice for gals' profile pics."We were sitting on a treasure trove of data," said Sam Yagan, co-founder and CEO of Ok Cupid.
''There are millions of experiments essentially happening on our site every day."Yagan and his colleagues catalogued more than 7,000 profile photographs from Ok Cupid.com, looking at facial attitude, such as whether the person is smiling; context of photo, such as whether the image was taken outdoors or in a bedroom; and how much skin is bared.
Many photographs of soldiers were taken during World War I and were sent home in postcard form.
Studio photographers are sometimes stated on the mount or stamped on the back of photographs and in some cases can be researched to reveal the studios operational dates.