One of the most famous photographers from the mid-1800s was Nadar who established the most fashionable portrait studio in Paris – it was here that the Impressionists held their first exhibition in 1874. His actual name was Gaspard-Félix Tournachon, 1820-1910. The model is Marie-Christine Leroux (aka Mariette), they take the photo in ~ 1860-1861. The first letter of the signature is interesting because it is the same than the logo we find on postcards attributed to Paul Nadar (1856-1939), his son.