This was the predecessor to the modern photograph. It dated from the 1840s and 1950s, when it was super-ceded by better methods.
Daguerreotypes are the classic “old style” of photograph, which appear to be shot through a sepia or silver filter.
Why I Looked It Up
From Uncle Tom's Cabin:
It was a daguerreotype, clear and soft as an engraving, representing Eva and her father sitting hand in hand.