Fresno police have "just scratched the tip of the iceberg" in their investigation of charges that an elementary school principal took pornographic pictures of female students, a department spokesman said. The principal, Loren K. Ebersole, 55, has resigned in the wake of a criminal complaint charging that he photographed third- through sixth-grade girls at Burroughs Elementary School in various stages of undress. Investigators who searched Ebersole's home found other photographs of "still-unidentified females," Sgt. Richard Desmond said. Officers seized "thousands of pictures," he said, including some video cassettes. Police said the pictures appear to have been taken in school settings. During a career of more than three decades with Fresno Unified School District, Ebersole taught at six elementary schools and was principal at four others.