Chief Brian Cummings said 13 years ago, he posed for pictures with a woman in a bikini.
Cummings called his part in the photo incident "irresponsible and inappropriate" and said he came forward with the picture for accountability.
He has apologized and plans to perform 120 hours of community service as a self-imposed punishment.
His department is already under fire for videos showing adult film stars posing on fire trucks.
Mayor Antonio Villaraigosa said he accepts Cummings' apology.