Teens sharing nude or provocative photos is not brand-new, says Dr. Richard Chalfen at the Center for Media and Child Health, and there are “at least 4 kinds of sub-cultures crucial to understanding the ‘sexting’ phenomenon”; “media culture,” “digital culture,” “intense visual culture,” and “adolescent culture.” Chalfen explains each one in “Teen Culture,” the first of a very digestible three-part series. In Part 2, “Photo Sharing Behavior,” he gives examples of “sexting” past, then talks about influences of the current media environment, including reports of adults misusing cellphone cams, intimate paparazzi photos of celebrities, ethically challenged citizen “photojournalists” and even professional photojournalists, reality TV, graphical language and stories in talkshows, and the general blurring of public and private. In Part 3, Dr. Chalfen discusses some of the consequences, with an eye toward family discussion. A related new resource – another project of the Center, a joint venture of Children’s Hospital Boston, Harvard Medical School, and Harvard School of Public Health – is “Ask the Mediatrician,” where people can email media-related child-health-related questions to and find in-site answers from Dr. Michael Rich, a pediatrician, parent, and director of the Center. It’s a brilliant concept. I’d just like to see a search box in the site and – in answer to a question about Internet safety – a link to research down the street at the Harvard Law School’s Berkman Center, “Enhancing Child Safety & Online Technologies,” which found, among other things, that a child’s psychosocial makeup and environment are better predictors of online risk than the technology the child uses.