The first image shows two teenage girls lying side by side in their bras. One of them is talking on a phone, while the other makes a peace sign.

In another picture, a third girl is seen just as she emerged from a shower, wrapped by a towel but with her breasts exposed.

Not quite the stuff of X-rated movies, but it was enough to prompt the Wyoming County district attorney last month to threaten to file charges of child pornography against the three girls involved unless they agreed to probation and a 10-hour "re-education program."

The girls' parents did not agree to the probationary program, and instead filed a federal lawsuit yesterday against District Attorney George Skumanick Jr., accusing him of retaliation and abuse of power in the case of "sexting" -- sending nude or sexual photos by cell-phone text-messaging, a practice increasingly common among teens.

The parents are asking a federal judge to prohibit Mr. Skumanick from filing any charges. A hearing is scheduled for this afternoon.

"Kids should be taught that sharing digitized images of themselves in embarrassing or compromised positions can have bad consequences, but prosecutors should not be using heavy artillery like child-pornography charges to teach them that lesson," said Witold Walczak, legal director for the ACLU of Pennsylvania, who filed the lawsuit on behalf of the students. "These are just kids being irresponsible and careless; they are not criminals and they certainly haven't committed child pornography."

Mr. Skumanick disagrees.

"I simply wanted to get across to them just how dangerous this really is," he said. "Once these [pictures] are out there, they don't go away."

Mr. Skumanick believes that offering the students the class, developed in conjunction with his victim-witness resource office, was "the right thing to do," to address "a foolish act."

The case came to light in October, when school officials in the Tunkhannock School District seized a number of student cell phones. They examined them and found images of scantily clad and naked teenage girls, many of whom were enrolled there, the lawsuit said. Male students had been trading the images on their cell phones, the district said.

On Feb. 5, Mr. Skumanick sent a letter to the parents of about 20 students, informing them that the children could be charged with possession or dissemination of child pornography because of the pictures.

He offered to them the chance to avoid charges by entering a re-education program and serving a term of probation. All of the students, except for the three named in the lawsuit, agreed to the terms of the deal.

John Burkoff, a professor of criminal law at the University of Pittsburgh School of Law, believes that by threatening charges against the girls, Mr. Skumanick is losing sight of the proper role of a prosecutor.

"What they did was clearly immature but I don't think it was criminal. Worse than that, I think the role of a prosecutor is to protect the community interest, but these girls are a part of his community," he said.

If the girls are charged and convicted of child pornography violations, the plaintiffs contend, they would have a felony record and could be subjected to state Megan's Law provisions, which would require them to register as convicted sex offenders.

"That's a heck of a lesson for a kid who probably doesn't even realize she is doing something wrong," Mr. Walczak said.

According to a study cited in the lawsuit, sexting is widespread, with about 20 percent of teens 13 to 19 having done it.

Sexting is not a sign of deviance or a future indicator that teens will become sex offenders, said Christopher J. Ferguson, a psychology professor at Texas A&M International University who studies how media and technology affect youth.

Mr. Ferguson called sexting a "normative, not wise, sexual behavior on the part of these kids. We would have done it, too, if we would have had the cool phones. We didn't do it because we didn't have the technology."

Mr. Ferguson believes the students do need to understand the consequences. But punishment should be meted out by their parents with sanctions like grounding or taking away their cell phones. He added that the idea of a class is "not horrible."

As part of the five-week, 10-hour program Mr. Skumanick recommended, girls would "[g]ain an understanding of how [their] actions were wrong," "gain an understanding of what it means to be a girl in today's society," and "[i]dentify non-traditional societal and job roles."

There is a separate class for boys.

While Mr. Skumanick has threatened charges of child pornography against some students, he has not raised the specter against any of the people who had the pictures on their cell phones, the lawsuit said.

Further, when the girls' lawyers asked to see the pictures, Mr. Skumanick refused, contending that "they are 'child pornography' and that he would be committing a crime by sharing a copy," the lawsuit said.

Attorneys representing the girls believe that the photographs, which depict no sexual activity or genitalia, are protected expression under the First Amendment.

"Skumanick's decision to prosecute the subjects of the photographs, the three plaintiff minors, is unprecedented and stands anti child-pornography laws on their head," according to the lawsuit.

But it's not unprecedented.

Three boys from Southmoreland High School in Greensburg were charged this year in juvenile court with possession of child pornography after the school discovered racy pictures of girls on a confiscated cell phone. Three girls in the photos were charged with possession, manufacture or distribution of child pornography.

All of the students charged agreed to accept lesser misdemeanor charges, said Westmoreland County public defender Dante Bertani, who represented five of the students.

The students agreed to probation and a class where they learn that they "shouldn't be sex texting," said Mr. Bertani. "It's insanity. Law enforcement gets carried away with what they believe is their duty to find everyone who spits on the sidewalk guilty of murder."