The secretive world of child exploitation is in the spotlight because of an arrest last week in the 1996 murder of JonBenet Ramsey, a 6-year-old beauty pageant princess. The suspect was a fugitive from charges of possessing child pornography and had exhibited a fascination with the sexual abuse of children.

While many of the recently created sites are veering into new territory, the concept of for-pay modeling sites using children has been around for years. They first appeared in the late 1990’s, when entrepreneurs, and even parents, recognized that there was a lucrative market online for images of girls and boys.

Sites with names like lilamber.com emerged, showing photographs of children, usually modeling in clothes or swimsuits. Their existence set off a fury of criticism in Congress about possible child exploitation, but proposed legislation about such sites never passed.

The sites that have emerged in recent months, however, are markedly different. Unlike the original sites, the newer ones are explicit in their efforts to market to pedophiles, referring to young children with phrases like “hot” and “delicious.” The children involved are far younger, and the images far more sexual, emphasizing the minors’ genitals and buttocks

Some modeling sites have already attracted the attention of law enforcement. Earlier this year, prosecutors obtained a guilty plea on child pornography charges from Sheila L. Sellinger, then of Shoals, Ind., who had been selling illegal photographs of her 10-year-old daughter on a modeling Web site. Last month, Ms. Sellinger was sentenced to almost 12 years in prison.

Ms. Sellinger, who earned thousands of dollars a week from the pornographic yet clothed images of her daughter, cooperated with law enforcement, leading to the arrest of two men who had been assisting her with her site and had been running several more, court records show.

To attract subscribers, central marketing sites, called portals, list scores of available modeling sites that accept money in exchange for access to children’s images. The portals promote the busiest sites, ranking them by the number of hits they receive.

Such a marketing approach proved effective for some online child pornography businesses that have disappeared over the last year, including those that offered illicit videos of children generated by Webcams.

The Times did not subscribe to any sites, which it first saw referenced in online conversations among pedophiles. The Times followed a link posted in those conversations to forum postings and images on freely accessible pages of the modeling sites. Because those sites appeared to be illegal, The Times was required by law to report what it had found to authorities. Federal law enforcement officials were notified in July about the sites.In contrast to their advertising, many of the sites portray themselves on their main pages as regular modeling agencies trying to find work for their talent. But executives in the legitimate modeling business said that virtually everything about the sites runs contrary to industry practice. Most child images for genuine agencies are password-protected, the executives said, with access granted to companies and casting agents only after a check of their backgrounds.

These executives said that real modeling agencies would refuse to use the types of sexualized images of children sought by pedophiles, not only because they are exploitative and illegal, but also because they would be bad business.

Such images on an agency Web site would drive away many parents who might be seeking representation for their child, executives said; indeed, most photographs of child models are nothing more than head shots. And the legitimate agents provide the phone numbers, addresses and names of their executives so potential clients can contact them; most of the sites aimed at pedophiles not only provide little or no means of contact, but even hide the identities of the owners behind anonymous site registrations.

“These are clearly not bona fide companies, and it’s obvious these are just Web sites for people to go on and view children in an unhealthy manner,” Bonnie Breen, chief booker for the Bizzykidz Agency, a prominent modeling agency for children based in London, said when provided with a description of the emerging modeling sites.

Despite repeated statements on the sites that they are lawful, they may well run afoul of American law. While the issues are far from settled — thus leading to the attempts by Congress to clarify the law — courts have worked over the last two decades to define standards for what constitutes potentially illegal images of children.

‘Lascivious Exhibition’ Standard

Under law, for an image that does not involve a child engaged in a sex act, a court must find that it entails “lascivious exhibition of the genitals or pubic area” of a minor to determine that it is child pornography. As a result, courts have ruled that images of naked children were not automatically pornographic, and thus not illegal, while also holding that the mere presence of clothing on a photographed child was not, in itself, adequate to declare the image lawful.

Instead, the courts often apply a six-pronged test, developed in a 1986 case called United States v. Dost, to determine whether an image meets the “lascivious exhibition” standard. That test — which requires a court to examine the child’s pose and attire, the suggestiveness and intent of the image and other factors — includes one standard on whether the child is naked. However, no single standard under Dost is absolute, and courts must continuously examine potentially illegal images while considering each part of the test.

The leading precedent on child pornography involving clothed minors is a federal case known as United States v. Knox, which involved a pedophile who obtained erotic videos of girls. In that 1994 case, the Federal Court of Appeals upheld the conviction of the pedophile, Stephen Knox, saying explicitly that clothing alone did not automatically mean that images of children were legal.

“The harm Congress attempted to eradicate by enacting the child pornography laws is present when a photographer unnaturally focuses on a minor child’s clothed genital area with the obvious intent to produce an image sexually arousing to pedophiles,” the court’s ruling says. “The rationale underlying the statute’s proscription applies equally to any lascivious exhibition of the genitals or pubic area whether these areas are clad or completely exposed.”

While adult pornography has some First Amendment protections, there are no such protections for child pornography. Still, some experts have expressed discomfort, in general, at criminalizing clothed pictures of minors.

“This is a difficult area,” said Michael A. Bamberger, a First Amendment specialist at Sonnenschein Nath & Rosenthal, based in New York, who filed a brief on behalf of a booksellers’ group in the Knox case. “The whole history of the exception from First Amendment protections for child pornography is based on the harm to the child. But there is in my view a free speech issue with respect to designating photographs of persons under the age of 18 who are clothed as child pornography.”

But Mr. Bamberger expressed uncertainty about whether his concerns applied when told details of the model sites found by The Times. “To me, it sounds as if you are really talking about nude equivalents, almost like cellophane clothing, and that’s not clothing at all.”To distinguish between illegal images and, say, photographs of children posing in underwear for a store catalog, the court said it had to apply the Dost standards and review a range of facts, like the nature of the images and whether the marketing was intended to appeal to pedophiles.

For example, the court noted, a potential customer could know the images of minors were illegal if they were marketed with statements proclaiming that they would “blow your mind so completely you’ll be begging for mercy.” Explicit listing of the children’s ages, along with sexually loaded terms like “hot,” could also be used as evidence of illegality, the court said.

The modeling sites reviewed by The Times incorporated many such references to encourage viewers to subscribe.

That is true for one of the most successful collections of sites, according to some portal rankings, run by an entity called PlayToy Entertainment. On its central site, PlayToy holds itself out as a company that helps children start modeling careers. There is, however, no phone number, address or prominent e-mail address available for companies that might seek to hire the girls or for parents who might want their children to be models.

The central PlayToy site originally located by The Times contained links to as many as six sites featuring little girls. In recent days, the central site has been redesigned, removing the links to the girls’ individual sites.

Those sites still exist, however, including the one for the girl called Sparkle. Another site features a prepubescent girl named Lolly — a widely used online code word for pornographic images of girls. There are even sexualized images of a girl called Baby, who appears younger than 5 and whose photographs seem to go back as far as her second birthday or earlier, when she was still in diapers.

The marketing makes clear that this is no typical modeling company.

“Call 911 before viewing!!!” proclaims the site for Sparkle, which shows her in a thong so revealing that she appears to be naked below the waist. The ad for the site uses words that echo those cited in the Knox decision, reading, “Only 9 years old! Hot!”

Other PlayToy sites are more explicit. “Feel her breathe on your face, take a gentle touch from your screen, open your mind and push the limits,” reads the site for the girl called Lolly. “If you are ready to handle this trip, PlayToy Lolly is calling.”

An advertisement for another PlayToy site, featuring a girl called Peach, declares, “A peach has never looked so delicious.**8 years old**.”

The site includes a picture of the young girl wearing a tank top pulled off one shoulder. Directly below that is a purple emblem with the company name and the words, “Nonnude website: 100% legal.”

But experts said that assurance was almost certainly not true. Based on the ages of the children, the marketing words and customer comments on the PlayToy sites described to him by The Times, a lead lawyer in the Knox case said that the subscribers had plenty of reason to worry.

“They shouldn’t have any comfort that they are not breaking the law,” said Edward W. Warren, a partner from the Washington office of Kirkland & Ellis who helped to argue Knox as a representative of 234 members of Congress who joined the case. “This sounds worse and more graphic and more grotesque than what we were dealing with, particularly given how young the children are.”

The assurance by the company that the sites are lawful is irrelevant to any potential prosecution, experts said. Indeed, in the Knox decision, the court held that defendants could be found guilty if they were aware of the “general nature and character” of images that they bought involving clothed children in sexual poses.

“The child pornography laws would be eviscerated if a pedophile’s personal opinion about the legality of sexually explicit videos was transformed into the applicable law,” the court held.

In their comments on PlayToy’s site, which can be viewed without registering with the company, the subscribers make clear that they are aware these are sites for pedophiles, not legitimate modeling clients.

“I think it would be awesome to have the models start off fetchingly clothed, and then strip down to tops or panties (or thongs!!),” a customer calling himself head2fat wrote on the forum.

Another client, calling himself ludwig66, instead requested that the girls appear in stockings, “ending up removing them to reveal bare feet and legs.” And still another customer, calling himself littlefeet, asked the site owners to pose the girl known as Baby in bare feet with her toes pointed, “so all of those beautiful wrinkles show!!!”

While PlayToy’s management and its members repeatedly assure themselves online about the legality of their images, they did not hesitate to post images from known child pornography sites. For example, when Ms. Sellinger was arrested this year for selling photos of her daughter, PlayToy members — and even the site operator — posted messages of dismay, referring to both mother and daughter by name. They also composed a photographic homage to the girl in the forum discussion, using images from the site that had been deemed illegal.

PlayToy’s sites have been online since October, company records show. But in that short time, the records show, 6,000 people have subscribed to view the images of the girls. Each subscriber is paying $30 a month for each site; that means the operators have collected a minimum of $180,000 in that short time, assuming every subscriber bought only one site for one month.

The cash has been collected either by credit card — processed through a company called Advanced Internet Billing Services, or through Western Union payments — as well as through an online money system called e-gold.

A Tortuous Digital Trail

Attempts to learn the identities of the people behind PlayToy suggested many possible locations. Payments through Western Union were processed through Ukraine. An administrative e-mail address suggested the company was based in Russia. Using a commercial software program, The Times traced messages sent by the PlayToy sites back to servers in Germany and obtained what is known as the Internet protocol address of that online host.

An examination of the registration documents for the sites’ names led to a company that is essentially a front, permitting its name to be used as the registrant by people who wish to remain anonymous.

The Times then obtained business records about the site prepared by someone involved in its operation.

If true, the records show the name, address, telephone number and other personal information of a man in Florida who is involved in running the site. An e-mail address listed in the records was traced to postings that appeared in pedophile conversation sites, including comments praising child pornography and images of young girls in thongs. Because of the possibility of identity theft, The Times has elected not to publish the name of that man or of associates who also appear to be involved in the business.

The Florida man did not return a voice mail message left on his cellphone or respond to an e-mail message.

Still, even if the operators of PlayToy are positively identified and compelled to shut their sites, the growing business of model sites would probably continue to thrive. PlayToy’s many subscribers, a large number of whom identify themselves on the site as living in America, could simply drift over to other model sites, all offering similar fare.

There, on each of those hundreds of competing sites, the subscribers will find at least one other little girl who, every few days or so, is dressed in panties or thongs, placed in a bathtub or posed on a bed, while a nearby adult snaps pictures for the delight of a paying audience of thousands.