Below is the PSA classification for photo types:
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).
Type 1 photographs are the most desirable and valuable of the four photograph types because of their vintage and originality.