An outdoor ad campaign in San Francisco is trying something novel to stop people from texting and driving: public shaming.

Graphic designer Brian Singer has furtively been taking photos of people texting behind the wheel along the 101 Freeway and posting them to a website, Texting While in Traffic, or TWIT for short. (Singer says he's always a passenger, not a driver, when he snaps the photos.) Lately, Singer has been paying out of his own pocket to put some of the photos on billboards around town, Gizmodo reports.

He says the number of offenders is outrageous. "For every nose picker, there's 20 texters," he estimates. He's not bothered by privacy concerns, either. "I don't think people driving on 101 have the expectation of privacy," Singer says. "All I'm really doing is taking photos in a public place."

Singer tried to get a road-safety group to fund the project, but is going it alone for now with 11 billboards. He says he hopes the billboards freak people out enough to stop texting and driving—and even hopes other people start taking photos, which "could have a dramatic affect on people's behavior."