In Iowa, Jorge Canal is on the sex offenders registry because, at age 18, he was convicted of distributing obscene materials to a minor after he sent a picture of his penis by cellphone to a 14-year-old female friend who had requested it.

In Florida, Phillip Alpert, then 18, was charged with distributing child pornography and put on the sex offenders registry because after a fight, he sent a photograph of his nude 16-year-old girlfriend by e-mail to dozens of people, including her parents.

In most states, teenagers who send or receive sexually explicit photographs by cellphone or computer — known as “sexting” — have risked felony child pornography charges and being listed on a sex offender registry for decades to come.

But there is growing consensus among lawyers and legislators that the child pornography laws are too blunt an instrument to deal with an adolescent cyberculture in which all kinds of sexual pictures circulate on sites like MySpace and Facebook.