A presumptuous photo someone takes of themselves with something that they want, pretending like it belongs to them. See also: IYD pic
"Holy crap, did you see Jen's photos on Facebook? Her boyfriend proposed and bought her a monster rock!"
"In her dreams! That was just a shelfie."
"Matt just bought a new motorcycle!"
"No, he didn't; those were just shelfies. Two seconds after he tweeted that last one, the real owner came out into the parking lot and threatened to put him in the hospital."