Magnus: The Shazam of the fine arts world

Standing in Pace MacGill, an art gallery in Manhattan, the art market researcher-cum-entrepreneur Magnus Resch opened an app on his iPhone and beamed. "Take a picture of an artwork," he said, handing over his phone, which displayed a salmon-red and white interface bearing the logo "Magnus".I did and then touched a button on the screen and the artwork in question - a 1973 image by the photographer Hiro, which was presented without a label on the gallery's wall - appeared on the phone, correctly...