ALLENTOWN — Police faced a difficult if not impossible task Thursday as they tried to stop the spread of pornographic video and photos of two high school girls, images that were transmitted by cell phone to dozens of the girls' classmates and then to the wider world.

District Attorney James B. Martin said at least 40 Parkland High School students believed to have received the images would not face prosecution as long as they show their phones to police by Tuesday to ensure the images have been erased.

But students at the school said the distribution was far more widespread.

"Most people got it and kept passing it along for fun to everyone in their phone book," said Jon Gabriel, 16, a junior who said he received and deleted the images.

A state trooper was sent to the school Thursday and will return for two more days to ensure that images were erased from the cell phones of students whose parents got letters from prosecutors. The letter explained what had happened, set a deadline for erasing the images and asked the parents to sign consent forms.

Martin said students who fail to comply by the deadline could be prosecuted in juvenile court for possession of child pornography.

One of the girls in the pictures is shown engaging in a sex act with an unidentified boy, Martin said. The other girl took and transmitted a photo of her bare breasts, he said.

Martin said he was not certain if the girl shown having sex "knew at the time the act was being performed that she was being photographed."

As for the other student, "she's a victim, and she's not a victim," he said.

"Our thrust has been to get the kids to come forward, and we've indicated we will not charge them for possessing the images," Martin told The Associated Press. "I'm not sure what we're going to do with the participants at this point."

Students interviewed at the school Thursday said the pictures made the rounds about two months ago and that the images have been distributed everywhere — to Temple and Harvard universities, to a high school in Bethlehem, even to someone in Oregon.

"The school isn't going to get everybody because it is everybody. I don't know anybody who didn't get the pictures," said Samantha Smith, a 16-year-old junior who said she deleted the images when she got them.

Senior Nicco Delnero, 17, said teachers discussed the episode with students, "telling us how it could hurt the girls in the future."

Authorities began investigating about two weeks ago after some students notified school administrators, Martin said.