There are two types of cased images you might find in your family collection: ambrotypes and daguerreotypes.
The quick and easy way to tell the difference between the two is that a daguerreotype will look like a mirror when you move it in the light. An ambrotype will not.
I was thinking about this today when I put away an ambrotype I purchased on ebay. It was listed as a daguerreotype. I don't think this was a deliberate deception, just ignorance.
For more information about these hauntingly beautiful cased images, check out Wikipedia's entries for ambrotype and daguerreotype.
The daguerreotype entry says this:
Wait a minute...
Daguerreotypy continues to be practiced by enthusiastic photographers to this day, although in much smaller numbers; there are thought to be fewer than 100 worldwide. Its appeal lies in the "magic mirror" effect of light reflected from the polished silver plate through the perfectly sharp silver image, and in the sense of achievement derived from the dedication and hand-crafting required to make a daguerreotype.
There are artists who use these historic photo processes today?
Talk about a beautiful anachronism! I would pay oodles of money for a daguerreotype or ambrotype of an iPod. Not that I have a budget for that kind of frivolity, but still. The Wiki has several links to these contemporary artists if that idea intrigues you, too.
[photo credit] "Erika" Ambrotype on black glass by artist/photographer Quinn Jacobson. Made May 2007, Viernheim, Germany.
UPDATE: OK. Forget what I said about the iPod. That was just the first thing that came into my head. What I really want is to see a daguerreotype or ambrotype of the Neverwas Haul.