What’s the Difference between a Selfie and a Self-Portrait?

A selfie is a self-portrait taken with a smartphone. At least, that’s what I assumed until two weeks ago when I stumbled on an article in The Guardian about the Getty exhibition In Focus: Play. “You do see self-portraits,” curator Arpad Kovacs said of the show, “but they are self-portraits rather than selfies.”

Instantly curious, I asked him to elaborate on the difference (emphasis mine):
The self-portrait and the selfie are two separate, though at times overlapping, efforts at establishing and embellishing a definition of one’s self.