One thing to remember is that 1860s studio photos had plain backgrounds, in particular a plain wall. At most, there might be a nearby chair or table. Lots of ornamental stuff in the background, like a painted window and tree on the wall or painted forest or farmland, is more modern. The 1890s photos often had painted scenes behind the person.
Below is an 1860s cdv with nothing on the wall, and just a chair next to her. The blank wall in particular is period.
Below is an 1890s cabinet card with a busy, ornate and frilly background. The background is just a painting in the studio:
