There are some interesting buried comments in a Mar 22, 2019 Artsy article by Karen Chernick on the collection of Michael Mattis and Judy Hochberg (now on display at the Barnes Foundation), which briefly describing a few modern methods of detecting 19th and early 20th C photographic fakes and reprints. The two collectors developed the techniques in consultation with a paper conservator.
When the duo started their collection, prices were rising at a fever pitch, but the market had few safeguards for determining whether or not a photograph was actually vintage. The need for dating tools became evident in the late 1990s, when a suspicious number of purportedly vintage prints by Lewis Hine—an American photographer who recorded child labor conditions and made portraits on Ellis Island—flooded onto the market.
The couple determined that their purportedly vintage Hine photographs were posthumous in part because the paper was bleached, a practice that only began in the 1950s when manufacturers began adding optical brighteners to paper.
Messier, Hochberg and Mattis’s collaborator on the scientific tests, also developed a watermark cheat-sheet to help determine the age of photographic paper. The Agfa logo, for example, has changed over the years, and knowing the year range for a particular version can help date a photograph. The tools Messier helped the couple develop for their own collecting purposes have now become industry standard.