In his photos, Smith appears a bit dour, distant, stern, etc. - lacking of friendliness or personality. Maybe that's how passenger ship captains then were expected to look? Or maybe it was just the culture and sign of the times?
I've not seen too many photos of people from that era where they were smiling to be honest. It wasn't a "say cheese for the camera" thing. Smith was a popular captain, especially amongs the first class passengers, so I doubt if he was lacking in social grace.
I've gone back to some photos of Smith. I think I was influenced by his beard and drooping mustache, which to my modern eyes, gives him the appearance of a scowl. Nowadays, not a particularly good look. But I shouldn't have drawn my original conclusion.
According to Walter Lord, he wasn't short of a charachter, only allowing company, while smoking, if it only promised to stand completely still so not to disturb the cloud of smoke floating above his head.
As a student of the history of photography, I believe it is a misnomer that it was rare to smile in a photograph in Titanic's time. I have seem many daguerreotypes of the 1840s and '50s showing persons smiling.
Incidentally, I never smile in photos. Unless instructed to do so.