A federal initiative that publicizes photographs of unidentified child molesters led to a life sentence for a five-time sex offender from Harrisburg, federal officials said.

In a case involving about 200 pornographic pictures, James A. Reigle, Jr., 46, was convicted in December of sexually exploiting minors to produce child pornography, conspiracy to transport child pornography and shipping child pornography. He was sentenced last week.

"As far as we know, this is in fact the first life sentence imposed for a child pornography offense," U.S. Attorney Rod Rosenstein said.

Mr. Reigle, of Harrisburg, was arrested after an investigation by the Endangered Child Alert Program, which was created in 2004. The program enables investigators to obtain an arrest warrant for a child molester without knowing the identity of the suspect. The initiative, which allows authorities to get a "John Doe" warrant based solely on a photograph, is part of the FBI's Innocent Images Task Force based in Baltimore.

Photographs of suspects are also put on the FBI's web site.

Raul Roldan, the chief of the FBI's cyber-crime section, said investigators have been able to identify and arrest five of six "John Does" and one "Jane Doe" under the program.

"Furthermore, more than 30 previously unknown child victims have been identified and rescued," Mr. Roldan said.

The investigation into Mr. Reigle began in 2003 when an FBI agent downloaded an Internet photo of a man and a boy engaged in sexually explicit conduct. Authorities didn't know the man's identity, so investigators submitted an image to the television show "America's Most Wanted." After it aired, the man was identified as Thomas Evered, of Lolo, Mont. The man's sister saw the image on the program and told his mother, who talked him into turning himself in.

Agents then found that Messrs. Evered and Reigle had been taking pornographic photographs of teenage boys and trading the images to each other over the Internet. Federal agents also found out about a third man, Loren Williams, of Edgewater, Md., who was sentenced to 15 years for producing pornography.

Mr. Evered pleaded guilty to sexually exploiting a minor to produce child pornography and received a 10-year sentence after agreeing to testify against Mr. Reigle.

Prosecutors said Mr. Reigle developed relationships with several boys between 1998 and September 2002 and took pictures of them engaged in sexually explicit conduct.

Mr. Reigle was sentenced in 2002 by a federal judge in Harrisburg to a 37-month federal prison term for possessing child pornography. He was convicted three previous times on child pornography in Pennsylvania state courts.

Two aspects of the case gave Maryland investigators jurisdiction. Some of the pornography was carried through Maryland by Evered, who was a truck driver, drove his tractor-trailer through Maryland. FBI agents also viewed the pornography while in Maryland.

"So criminals who think that they're safe from committing criminal activity because nobody's going to know where they are going to learn a lesson here," Mr. Rosenstein said.