When human remains are found, the skull is sometimes sent to Petersen so that he can recreate the face. This will only be done if dental records do not provide any clues to the decedent's identity. Before he can begin rebuilding the face with clay, Petersen must use the information from the forensic anthropologist to determine tissue depth. The statistical information has been compiled over a number of year by using people who have been killed in wars or car accidents. Rounded erasers are then cut, numbered, and glued on various areas of the skull to act as markers for identifying the tissue depth in a given area. Clay is layered from the lower marker to the higher marker, following the contour of the skull, the shape, and also the thickness of the tissue. The reconstruction of the eyes, nose, and lips requires special techniques for each feature. Eye and hair color can only be determined by using clues from the investigation. In addition to skull reconstruction, Petersen uses a computer program to perform age progression for the identification of children who have been missing for years. This is done with the aid of photos of the parents as they progressed through various ages of childhood. Petersen also does photo comparison work, which is often done when someone is applying for landed immigrant status and the photo they provide looks nothing like them, or they could be attempting to renew their passport and they look different from their photograph. Petersen has been involved in a project with the University of British Columbia, which would use CAT scans or lasers to scan a skull. Along with data on tissue markers, this information is supplied for a computer program that does the connection work.