When a gun is used in a crime, forensic investigators identify it by the unique pattern of scratches that its barrel leaves on bullets. A similar trick is now being used to match digital images to the cameras that captured them, an important advance as child pornography crimes increase.

Software developed by Jessica Fridrich at the State University of New York in Binghamton exploits the fact that every digital camera introduces a unique pattern of imperfections, or "noise," into its images. In monochrome areas, for example, individual pixels might actually be slightly different colors. Fridrich's software determines a camera's noise signature by identifying the irregularities in its pictures. That yields a "fingerprint" that investigators can search for in other photos.