Diana was killed in a car crash in Paris in 1997

The two are among three photographers charged with invasion of privacy following complaints filed by Dodi Fayed's father, Harrods owner Mohamed al Fayed.

Jacques Langevin and Fabrice Chassery said they were not aware they were breaking French law by taking photographs of Princess Diana and Dodi in their car before and after the crash in which six years ago.

A third photographer, Christian Martinez, also accused over the incident, did not attend Friday's trial.

Photographs unpublished

Mr Langevin, 50, said: "I am a witness. I was recording an event. I keep my feelings to myself."

An earlier attempt to prosecute the photographers for manslaughter for failing to give assistance to the victims of an accident failed.

Mr Langevin, of the Sygma/Corbis agency, Mr Martinez of the Angelis agency and freelancer Mr Chassery could get up to a year in prison and a 45,000 euro fine if found guilty.

I am a witness. I was recording an event. I keep my feelings to myself Jacques Langevin Paparazzi

Last year France's highest court found the photographers not guilty of having contributed to the crash, despite the paparazzi's high-speed pursuit of the car.

Instead a French investigation decided driver Henri Paul, was to blame because he was driving too fast and was under the influence of alcohol.

The photographers took pictures of Diana and Dodi in the car before and after the accident, though none taken at the crash site was ever published.

The case will centre on whether or not the inside of the couple's car should be considered a private space.

The charges were expected to relate only to the images of Dodi Fayed, as Diana's family are not party to the complaint.