More than 60 percent of the 500 largest U.S. companies have disciplined or fired employees for displaying, storing, or transmitting pornography or other improper images, according to a survey released last summer by Delta Consulting, in Atlanta. Many firms block access to pornographic Web sites, partly because pornography sent around the workplace can expose companies to sexual harassment lawsuits or charges of permitting a "hostile work environment." Other firms may limit their employees' Web surfing to a few preapproved sites.

But those two tactics do nothing to address images brought in as e-mail attachments, or those on CDs and USB storage devices, or, for that matter, MP3 players and cellphones, or those just e-mailed in by friends. PixAlert, a Dublin, Ireland, start-up, claims to be the first with software that can find pornographic digital pictures no matter how they enter the office PC. The program doesn't try to monitor pornography's myriad pathways into the workplace. Instead, it relies on the commonsense notion that the images aren't a problem until they're viewed, and when they're viewed they are patterns of pixels onscreen. The right algorithms can analyze those patterns.

PixAlert's software analyzes images for features the company says are characteristic of pornography. It distinguishes foregrounds from backgrounds, discerns the edges of individual shapes, picks out faces and bodies, and measures luminosity and texture. An image is given an overall score, and a high enough value indicates that the picture is likely to be pornographic, as opposed to, say, a photo of a beach scene accompanying a CNN story. When that happens, a report is created and sent to an administrator.

A second PixAlert product audits corporate networks, scanning every hard disk and analyzing every file. Most common file formats can be examined, though not encrypted files.

The software was introduced this past February, and so far the firm has shipped about 200 000 user licenses, mostly in the United Kingdom, Ireland, New Zealand, and the United States.

According to PixAlert CEO John Nolan, personnel managers began to worry about computer-based sexual harassment at almost the moment the Internet arrived in the workplace. In 1999 The New York Times fired 23 back-office workers for sending pornographic images via e-mail, and since then employees have been disciplined for sending—or just having—inappropriate text and images at Chevron, Dow Chemical, Xerox, and the U.S. Navy.

How useful the average company will find PixAlert's software is hard to say. Chevron's US $2.2 million lawsuit, for example, involved text, not images, so PixAlert's software would have been useless, as employees received material that could have led to charges of harassment. And the U.S. Navy's 1992 computer-related harassment cases, in which 500 people were disciplined, still paled in comparison to an unrelated 1991 sexual harassment scandal, which involved real-life physical abuse.

On the other hand there's Xerox, which fired 40 employees who spent, as a spokesman put it, "a majority of their workdays visiting inappropriate sites."