What were disadvantages of producing a photograph before 1839?

The only  two disadvantages I know is that the photographs when taking them were incredibly sensitive to movement and so they had to sit still for a long time and had to keep their eyes shut. The other disadvantage was that the person taking the photo could have contracted mercury poisoning.

Explanation:

this is not a question its simply asking you to read and write a few sentences and   the question on the bottom its fairly easy, you can do this!