A tool that helps websites track down and eliminate pornographic photos of children is now being deployed for law enforcement. Microsoft's PhotoDNA software, which matches images against a list of known pictures, will now be included in the free NetClean Analyze software already used by police, the Microsoft-developed Child Exploitation Tracking System, or through free individual licenses to agencies. PhotoDNA is already used by Microsoft's own web services to catch child pornography, and Facebook licensed the software last year. Police could potentially use it to scan public photo collections or go through evidence quickly.