San Bernardino County investigators were notified Tuesday and Big Bear High School employees and detectives began collecting the yearbooks in the mountain community at Big Bear Lake, 70 miles east of Los Angeles.
The school dance photo shows a 17-year-old boy's hand inside the clothing of a 15-year-old girl and may involve sexual penetration. Sheriff's spokeswoman Cynthia Bachman says the couple is in the background and went unnoticed by the yearbook adviser.
Bachman says most students have returned yearbooks for editing. Detectives are contacting students who haven't turned in yearbooks with a warning they could face a charge of possessing child porn.