Alexandra Zapruder was not born when her grandfather trained his home-movie camera on President John F. Kennedy's motorcade rolling through downtown Dallas 53 years ago, but that 26-second film has become a difficult family legacy.

On Nov 22, 1963, Abraham Zapruder, a devoted supporter of Kennedy and his vision for America, shot a home movie on 8 mm film that became the best-known moving image of the Kennedy assassination.

"Growing up, my parents didn't talk about this because it was grandfather's wish that we approach it with discretion and respect for Kennedy," Alexandra Zapruder, 46, says in an interview.

An immigrant Russian Jew who became a successful clothing manufacturer in Dallas, Abraham Zapruder went to Dealey Plaza to film Kennedy's motorcade, his granddaughter says.

He ended up capturing one of the most indelible moments in American history.

Growing up in Washington DC, where her father, Henry Zapruder, worked as a government attorney, Alexandra Zapruder, an author and member of the founding staff of the US Holocaust Memorial Museum in Washington, knew little of the film's back story.

She decided the family's complicated relationship with the film, which has been used in government probes, fueled conspiracy theories and been viewed by billions of people, may make for an interesting book.

Zapruder, who came to Dallas for the anniversary of the assassination to discuss her book on the film, Twenty-Six Seconds, says her family had always been guided by her grandfather's wishes to maintain the integrity of its deeply disturbing contents.

Abraham Zapruder sold an original copy and the rights to Life magazine for $150,000 to help tell the story of that fateful day in Dallas.

The magazine published several frames of the film days after the assassination. It did not surface again publicly until a version appeared on Geraldo Rivera's ABC-TV show, Good Night America in 1975.

Abraham Zapruder testified before the US government's Warren Commission investigating the assassination.

The commission concluded that a lone gunman, Lee Harvey Oswald, killed the president and wounded Texas Governor John Connally. Zapruder died in 1970.

Film rights returned to the family in 1978 and Zapruder says she watched her father juggle the demands for public disclosure with her grandfather's wishes "to do good with it", she says.

In 1999, the government paid the family $16 million plus interest for the original version of the film.

"He said he would have been happy to have never seen it again," Alexandra Zapruder says of her grandfather.