Police were alerted to the matter involving a "female victim "at the Bronzeville school Saturday, according to a department statement.
"Through conversations with students, the school official determined that a more serious crime may have been committed," according to a statement released Friday morning.
"At this time, the name of the victim has not been provided to police for an investigation, and there has been no evidence presented to police that a crime had been committed."
The photos were "distributed electronically" to some students, and police are seeking the name of the victim, which would allow "a proper investigation to be conducted."
Jeffrey Gray, President of Hales Franciscan, said the school has been cooperating with police over the course of the investigation.
"We've provided them with all the information we have. You don't hide anything from police," Gray said.
Gray said school employees heard rumors of the illicit photo circulating in late September and "took disciplinary action against a small group of students."
The school also warned parents and students about the legal ramifications of sharing illicit photos.
Parents who gathered outside the school Friday afternoon expressed concern over the allegations and support for the high school.
One parent, who refused to give her name, said her daughter is one of 13 girls at the school. She said her daughter told her about the photos in September and did not believe the girl in the photos was a Hales student.
Michael Smith, 52, graduated from Hales in 1979 and has sent four of his sons to the school. He said he was surprised to hear about the allegations.
"This is an institution of higher learning and this is coming from left field for everybody. It took everyone by surprise," Smith said.
Smith did not want to belittle the allegations, but called the incident a growing pain in the school's transition to a coed institution.
"When you have an all-male school and you open it up to women these situations will arise, but you never want to hear about it happening at your institution," Smith said. "But when it comes to sexual allegations with children you have to investigate the situation."
He said the allegations shed a negative light on the school, which he believes is a community landmark for its success in sending well educated men to college.
"We don't want it to happen, period, but one bad apple doesn't spoil the bunch," Smith said.