First smiling photograph EDIT THAT I WAS PREVIOUSLY AWARE OF: Eating rice, China (approx 1901-1904), collected by B. Laufer
I have always (well okay, since I saw it) loved this photograph. Especially the look on his face.
Shit i gotta go get some rice.
If I understand correctly, and there's a pretty good chance I don't, this was the first photograph that didn't have the subject standing solemnly.
edit: whoopsie