A woman who visited College Terrace Library on Sept. 22 said she saw a man viewing child pornography on a public computer.

On the screen were images of a young child, who reminded her of her daughter when she was 4 years old, other children and genitalia, she said in an email on neighborhood social network Nextdoor.

The woman notified the librarian during the Sept. 22 incident of the possible child pornography on a computer screen, and the librarian went to investigate, the patron said.

"I thought there must be laws protecting people from viewing porn at public libraries because the librarian clearly knew it was happening and only became alarmed when I mentioned it was child porn. Then I thought about how small that library is, and how you can see the kids section from the computer tables, and there are always kids gathered there for story hour and after school," she wrote.

Palo Alto police spokesman Capt. Zach Perron confirmed the department has an open investigation into the sighting, which was reported that afternoon.

"There is no information available for public release as we are still gathering information about what was allegedly seen. The alleged suspect is not known," he said in an email on Tuesday.

But he noted that library computers are open to the internet, and library patrons are free to look at whatever material they choose.

"The computers at our libraries have no filters on them to prevent access to certain sites that some consider to be inappropriate. With that said, looking at and possessing adult pornography is legal. Child pornography in all forms is illegal -- downloading it, viewing it, possessing it, making it, sharing it, and so forth, regardless of where someone may be viewing it," he said.

Library officials declined to comment on what actions staff took after being notified of the incident, citing the ongoing police investigation. But they provided a copy of the library's internet-use rules.

The policy states that: "Libraries and librarians should not deny or limit access to electronic information because of its allegedly controversial content or because of the librarian’s personal beliefs or fear of confrontation. The provision of access does not imply sponsorship or endorsement."

The policy further states the library does not restrict, filter or edit internet content, and it does not keep a permanent record of the webites visited or searches performed by individuals.

But the public-use policy also forbids engaging in illegal activity over the internet. It specifically notes state and federal laws pertaining to child pornography and content that is "harmful to minors." The federal 2000 Children's Internet Protection Act clearly defines pictures, images, graphic image files or other visual depictions that appeal to "a prurient interest" and describes either explicit or simulated sexual acts as part of the harmful content.

The Children's Internet Protection Act requires all schools and libraries receiving certain federal funding for internet access and computers to install filters on their computers to block access to "visual depictions" that are pornographic or harmful to children. But libraries and schools that do not receive those funds don't have to provide the filters. Palo Alto Library does not take the federal funds, city spokeswoman Claudia Keith said.

Palo Alto's library policy also forbids activity that creates a hostile work environment by displaying graphic or obscene images on computers in the library, which might create a hostile workplace for staff or may constitute a violation of the Title VII of the Civil Rights Act of 1964 which prohibits sex discrimination in the workplace.

The library's broad protection of access to content mirrors the stance historically taken by the American Library Association. In 2003, it fought a court case as defendants, arguing against the Children's Internet Protection Act. The association argued the act improperly required them to restrict the First Amendment rights of library patrons and that filters were inefficient.

A Library Association study found that filters fail to screen 13 percent of internet pornographic sites while denying access to important health information. A 2006 study of internet filters by New York University School of Law's Brennan Center for Justice also found that many filters were inefficient and screened out political and scientific material that was not at all related to pornography.

But the U.S. Supreme Court overturned a lower court ruling that the filters over-block content. The justices ruled the act was not unconstitutional and imposed a small burden on library internet users. Filters would not create any potential speech-related harm because libraries have the ability to unblock sites if adults so request, the court said.

Palo Alto Library's policy also states that providing connections to global information, services, and networks "is not the same as selecting and purchasing materials for a library collection." But the U.S. Supreme Court stated in the American Library case that the internet is "another method for making information available in a school or library." It is "no more than a technological extension of the book stack."