When it comes to pornography, much of the public's definition is right in line with former Supreme Court Justice Potter Stewart's 1964 definition: "I know it when I see it."

For internet filters, defining pornography is a little more complicated. And the filters don't always know it when they see it.

When County Executive Maggie Brooks threatened to cut funding for Rochester's Central Library, she said she was appalled that patrons could view "pornography" there. Under the library's policy, librarians can turn off computer internet filters if a patron over age 17 asks them to. It's a common policy across the country and one that some say has been required by the Supreme Court. Librarians argue that they have a duty to provide the public with all forms of information, as long as it's within the bounds of the law.

But filters aren't a fix-all for keeping illicit material off of library computer monitors. And the problem doesn't involve only graphic sex. Nor is the issue unique to the downtown library.

"There is an expectation that that these internet filters can see and block all," says Sid Pendelberry, a senior systems administrator and engineer at Rochester Institute of Technology. "It's just not so."

The boards of the Rochester Public Libraries and the Monroe County Library System have appointed a task force to study internet issues: legal as well as technological.

While the task force completes its work, internet access on all of the downtown library's computers are filtered, no exceptions. But for the inventive or the determined, racy or subversive material is not out of reach. Blocking software doesn't guarantee that patrons can't Google and oogle naked people. And no filter will. At best, filters will discourage those patrons or slow them down.

In 30 minutes at the downtown library ---with the filters on --- I easily accessed the following: lewd photos (at least in thumbnail collections through a Yahoo! image search); a website with instructions on how to counterfeit money, commit various forms of fraud, and build bombs; recipes for making crystal methamphetamine (one involved the use of a lava lamp); and graphic pictures of aborted fetuses.

Similar sites were accessible through the Fairport Public Library's computers. That's not a surprise. All libraries in the county system --- all of the city and suburban libraries --- use the same filtering hardware, 8e6 Technologies R-3000, says Patty Uttaro, assistant to the Monroe County Library System director.

At both libraries, filters allowed access to a pro-anorexia site, which proudly proclaimed: "Anorexia is a lifestyle, not a disease." They also allowed access to a site that chronicled user experiences with psychoactive substances --- everything from prescribed antidepressants to illegal hallucinogens.

At both libraries, the filters did block a number of sites that obviously contained explicit material.

But I also found that the filters allow access to legitimate medical sites on topics like breast cancer, sexual health, and commonly abused prescription drugs, such as Xanax, Oxycontin, and Methadone. It also allowed access to information on abortion, from both pro-choice and pro-life sources. A major criticism of filtering software is a supposed tendency to block useful information on certain health issues.

The filter also allowed access to non-medical sites on breasts and sexual health matters. The breast entry accessed on Wikipedia included a picture of a naked breast. Other sites included a Slate.com article about media attitudes toward certain sexual practices.

By their nature, internet filters are imperfect, though many experts say the technology has improved drastically since it was first developed. Filters rely on keywords, URLs, object analysis, or even image analysis. But rarely the latter, and there's a good reason.

Images are the hardest form of data to filter. Image-recognition systems don't work well, says Pendelberry. As an example, he says they can't distinguish between a woman wearing a bikini and a woman with no clothing. And the software and hardware is expensive and hard to implement. Humans are much better than computers in that regard.

But the filters do work, says Pendelberry --- at least as they are programmed to. Setting up a filter, configuring it, and maintaining it is just as important as picking one out, he says.

PUBLIC MEETINGS SET: The public libraries' internet task force has scheduled three meetings to take public comments regarding internet access issues: 6 to 8 p.m. April 12, Rundel Memorial Library downtown; 6 to 8 p.m. April 16, Gates Public Library; and 6 to 8 p.m. April 18, Fairport Public Library.