A selfie of Dahj and Soji
Wendy takes a selfie with Mariner
K'ranch taking a selfie with Brad Boimler
Quark in a selfie
A selfie was any picture someone photographed of themselves, often, although not always, with another person present as well.
In 2380, after it was learned that Beckett Mariner was the daughter of Captain Carol Freeman, Wendy forcibly took a selfie of herself with Mariner. Afterwards, the disheveled Mariner uttered, "Don't log that, alright. I don't want to see that up on the..." (LD: "No Small Parts")
In 2381, K'ranch participated in a Venarix hunt against Ensign Brad Boimler, which concluded with him taking a selfie with Boimler. (LD: "The Least Dangerous Game")
Quark charged a fee for autographed selfies with his fans in 2381. (LD: "Hear All, Trust Nothing")
In 2399, Soji Asha kept a photo of her and her sister Dahj Asha that was a selfie. (PIC: "The Impossible Box")