A few rookie questions about old photos

[Lordstan]

Well I am a novice to vintage photography as well.
This thread has many answers to your questions.
http://www.net54baseball.com/showthread.php?t=122360
Dr Cycleback's online PDF book will answer your questions as well as his course.

Another good reference would be this book
http://www.amazon.com/Portrait-Baseb...1713042&sr=8-1
Cowritten by Henry Yee and Marshall Fogel. (I just bought mine on ebay)

As I have learned, there really is an art form to telling the difference between photo types.

Companies like PSA/DNA and Beckett have started to grade and encapsulate pictures. Henry Yee and Marshall Fogel both consult for them doing authentication of photos.
http://www.psadna.com/photo_authentication.chtml

These are the current accepted categories, from PSA/DNA's web site:
Type I - A 1st generation photograph, developed from the original negative, during the period (within approximately two years of when the picture was taken).

Type II - A photograph, developed from the original negative, during the period (more than approximately two years after the picture was taken).

Type III - A 2nd generation photograph, developed from a duplicate negative or wire transmission, during the period (within approximately two years of when the picture was taken).

Type IV - A 2nd generation photograph (or 3rd or later generation), developed from a duplicate negative or wire transmission, during a later period (more than approximately two years after the picture was taken).

I am not recommending or endorsing any company, just linking them for information purposes.
Hopes that helps getting you started.
Mark