The National Police Agency has set up an automated system to find child pornography on the Internet.
The system is based on an NPA host computer that "patrols" the Internet periodically, checking sites for child pornography and cross-checking their images against an NPA database of images confiscated across the nation.
On finding a match, the NPA host computer automatically alerts police in the prefecture where the offending site is registered.
In June, the NPA put the system on trial use at police departments in Yamagata, Chiba and Okayama prefectures.
For its first catch, according to NPA officials, the system traced a 20-year-old vocational school student in Saitama Prefecture who published child pornography images on his Web site.
The site was registered in Yamagata Prefecture and the suspect was arrested in July on suspicion of violating the antiprostitution law for minors.
The system is also capable of tracing offenders overseas.
In August, Yamagata police traced child pornography that had been posted from Australia and circulated through a news group.
Australian police were notified via Interpol.