When nude photos of girls who attended a Baltimore County high school started showing up on a Web site, word quickly spread among students.

Eventually a county police officer stationed in the school got a tip and started investigating, and the images were taken down. But some of the girls’ parents wanted legal consequences for the boys who posted the photos.

The problem: The photos were “selfies” — images taken by the girls themselves and consensually sent to male students — and likely would not meet the legal definition of child pornography. Authorities determined that no legal action could be taken.

“Sexting” among teens, a practice considered by some experts to be a normal part of adolescence, is a vexing issue for law enforcement officials. Even with new laws outlawing “revenge porn” and “cyberbullying,” sexting is difficult to prosecute, not only because youth are involved but also because it’s not necessarily illegal.

Baltimore County State’s Attorney Scott Shellenberger said the incident “did not rise to a level of a crime, but certainly it was quite disturbing to the community and the school itself.” He recounted the incident, which occurred a few years ago, to illustrate a persistent problem, but he declined to name the school because he didn’t want to single it out.

Lt. Glen Wiedeck of the Baltimore County Police Department said the Crimes Against Children Unit estimated that the number of requests for authorities to investigate teen sexting has increased, reaching about a dozen in the past year.

“The last two or three years, it’s gotten significantly worse,” he said.

In most cases, rather than prosecute, law enforcement and school officials in the Baltimore region work to educate children about maintaining their privacy online.

“We ask the group the question, ‘Would you pull your pants down in front of your whole class?’ Because that’s what you’re doing,” Harford County State’s Attorney Joe Cassilly said.

Some prosecutors say their offices have pursued charges related to teen sexting, but they declined to disclose details because most cases were in juvenile court, where information is kept private.

Still, a number of incidents have garnered headlines.

At Milford Mill Academy in Baltimore County this year, school officials and police investigated nude images of students posted on Instagram. They concluded that no crime had occurred because the students who could be identified in the photos were not minors.

In July, prosecutors charged a 17-year-old Edgewater boy with distribution and possession of child pornography after investigators alleged that he posted sexually explicit photos to Instagram, many of them “selfies” taken by high school girls.

Anne Arundel County State’s Attorney Anne Colt Leitess said that case made it to court because the photos depicted minors engaging in sexual activity. She declined to discuss the case further because the boy is a juvenile.

“It’s a modern-day way to put someone’s name on the bathroom stall,” Leitess said. “What we’ve heard in our office is that the police field these calls constantly.”

But, she added, “It’s rare — very, very rare — that we have these kind of cases that actually get to court.”

Teen sexting has put law enforcement in the position of applying child pornography laws, which are somewhat subjective and carry hefty penalties, in cases involving victims as well as perpetrators who are young and often naive.

“You need to take [sexting] seriously because of the damage that these images can do to the child’s reputation,” said Jennifer Ritter, a senior assistant state’s attorney in Howard County who prosecutes sex offenses involving juveniles.

At the same time, discretion to prosecute “is important because you’re dealing with immature minds and immature decision-making,” she said.

Legally, child pornography depicts a minor in a state of sexual excitement, engaged in a sexual act, or posed in an explicit manner.

“Simply having a naked picture of someone under 18 is not a crime,” Leitess said. “A naked selfie is not pornography, just like a picture of a child on the beach running into the ocean without clothes on is not pornography.”

Officials say that even with new laws outlawing revenge porn and cyberbullying, the problem remains difficult to address.

Under both laws, prosecutors say they must prove that the perpetrator’s intent was malicious — a high bar.

Meanwhile, teen sexting has become more commonplace. Psychologist Jeff Temple, a professor at the University of Texas Medical Branch at Galveston who has studied sexting, found two years ago that nearly 70 percent of girls have been asked to send a nude photo of themselves. Boys were much more likely to ask for a nude photo than girls were, according to the 2012 study.

“If you have a teenage girl, chances are she has been asked to send a naked picture of herself,” Temple said.

And in a study released last month, Temple found that sexting usually precedes sexual activity. So while discovering sexting among teens can be alarming, it also can present an opportunity for parents to talk to their children about sex, he said.

Some experts say the legal system often isn’t the appropriate venue for addressing teen sexting.

Police and prosecutors “really do not have the resources to chase after sexting cases,” said Bob Lotter, creator of a parental monitoring app called My Mobile Watchdog, which allows parents to block Web sites and see whom their children are communicating with on their smartphones. Lotter said parents have a responsibility to monitor their children’s technology use.

“We do need to do something about it, but criminalizing child behavior — I would think most people would agree it’s not the way to go,” he said.

Adam Rosenberg, executive director of the Baltimore Child Abuse Center, also said parents have a key role to play. “We have to teach children about the appropriate boundaries. We need to be spending more time educating our children on the power of these devices.”

School officials have gotten involved. In Baltimore, Howard and Anne Arundel counties, officials said sexting and related issues, such as cyberbullying, are addressed in age-appropriate “digital citizenship” curricula.

“We try to counsel students and how to maintain your privacy,” said Dale Rauenzahn, Baltimore County school safety director.

Lt. T.J. Smith, spokesman for the Anne Arundel County Police Department, said police have taken an educational approach to the problem, encouraging parents to have frank discussions with their children.

“These are children, and we don’t want to put them in the criminal justice system, but we have to put an end to this type of behavior,” Smith said. “Kids have to be really aware of what they’re doing. The images are going to be out there for the world to see.”