This photo of a woman reading a book dates from the late 1850s. It can be dated by both the process used to capture the image and the image itself.
The photo is a one-sixth-plate ambrotype and pinchbeck metal mount in an original embossed leather case. According to Wikipedia: “Ambrotypes first came into use in the early 1850s … By the late 1850s, the ambrotype was overtaking the daguerreotype in popularity; by the mid-1860s, the ambrotype itself was supplanted by the tintype and other processes.” This image has been hand-tinted—which was common—to add gold-painted jewelery.
The hairstyle of the woman reading her book is distinctive. Her hair is parted in the centre, is severely-flat on top and sides, covering her ears, with straight sausage (or bottle) curls at her shoulders. This style was popular with younger women in just prior to 1860. (See here and here.)
The pose is (typically) formal for a studio photo. The background curtain has been washed out to a blank, the studio furniture is very basic. Most likely, the book is also a prop.
This is the oldest photo I have. I have seen earlier photos of people reading for sale, daguerreotypes from the early 1850s, but these are enormously expensive and so this is likely to stay my oldest photo!