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.