If you still need this, there are several options historically, as many different process were competing for use in that time. Each has Pro's and Con's, many of which were regional as they had to do with the expense/availability of materials and/or climate based complications. Most popular as far as I know were
Daguerreotype and
TinType, both of which are some various of a metal plate treated with various recipes of chemicals to make it light-sensitive, though the first photographs were actually on paper or white leather. The various advancements were mostly related to decreasing the required exposure time, which was necessary for use in portraits.
What are your story restraints. Pretty much anything behind a lens and treated with generic "salts" and "vapors" could be said to work, if you arent planning on actively exploring the resources that go into it. The major differences in terms of storytelling would be exposure time, plate material (metal or organic) and durability. Daguerreotypes for example were on expensive silver plates, but were so fragile they could be buffed off and reused (great for astronomers), or else needed to be stored behind glass for protection.