As you might already suspect, this isn't a surefire way of grabbing prints. It only works so long as you have access to high-quality snapshots of someone's digits. That's relatively easy with hand-waving celebrities and politicians, but it's far from guaranteed that someone will snap photos of your fingers while you're crossing the street. And of course, data thieves would still need to get your devices or otherwise find a way to sign in using your biometric info. The practical danger is low -- the concern is more that a determined intruder doesn't have to work quite so hard to get your secrets.