A few simple observations can help narrow the timeframe of an image.
Mats give us some wonderful clues as to a daguerreotype's (and ambrotype's) original date.
This material was called thermoplastic, as the mixture was heated and then formed in dies.
The cases themselves were called 'union cases', not in reference to the 'Union' side of the civil war, but the union of different materials that were used in the composite.
Note: These were used with daguerreotypes, ambrotypes, and tintypes General Rule: Thermoplastic or Union case dates after 1856.
The daguerreotype is very easily detected, even by someone who has never seen one before.
It exhibits the characteristics of a mirror at many angles.
These cases are not rare, but they did not dominate the daguerreotype market, probably due to price.
A thermoplastic case is recognized by its smooth plastic-like surface, one-piece construction (of each half) and brass hinges connecting the two halves.