Fact vs fiction: can doubts torpedo an Oscar movie?

More critically in awards season, can doubts about the truth of a film torpedo Academy hopes?

Or do Oscars voters not really mind as long as they get a good story?

For several of the pictures eyeing Oscars glory on Sunday, in theory based on real events, those are vital questions.

Director Ava DuVernay's Martin Luther King Jr movie "Selma" is accused of misrepresenting president Lyndon Johnson as an enemy of the civil rights icon.

Some critics have slammed "American Sniper," Clint Eastwood's movie about elite US sharpshooter Chris Kyle -- credited with killing at least 160 people in Iraq -- for allegedly glorifying a mass murderer.

Other recent films which generated polemics included "Zero Dark Thirty," which competed for the Oscars in 2013.

Some accused it of making a heroine out of a CIA agent who practiced torture, while others said it helped re-elect President Barack Obama.

That was the year that the Best Picture Oscar went to "Argo," about a bold CIA operation to rescue six US diplomats trapped in Iran by the 1979 hostage crisis.

The film, directed by Ben Affleck, was accused of playing fast and loose with the facts, notably failing to give credit for the major role Canada had in securing the US diplomats' freedom.

In earlier years Oliver Stone's "JFK" in 1991 and Ron Howard's 2001 movie "A Beautiful Mind" also fueled controversy.

"It doesn't help a movie to have controversy over it," said Tom Nunan, who produced the Oscar Best Picture "Crash" and who teaches at the UCLA School of Theatre, Film and Television.

Moreover, "it is not a coincidence that those controversies are happening now," when it could help to eliminate a rival in the crucial final stages of an Oscars campaign.

"Your competition is often responsible for pulling the tapestry out from under your feet," he told AFP.

Tom O'Neil, of the award season ranking and analysis website Goldderby.com, is more nuanced.

Members of the Academy of Motion Picture Arts and Sciences "are very tolerant of liberties screenwriters take and of the fact that a role can get sanitized," he said.

"I don't think the 'American Sniper' controversy could hurt Bradley Cooper," its main star, he added, saying: "It could even help him. Voters might want to help an American hero if they feel he's under attack."

"The Theory of Everything," about British astrophysicist Stephen Hawking, is another accused of taking liberties -- this time with chronology and mis-portraying his relationship with his first wife Jane.

O'Neil said: "It's a love story that's being told, people are rooting for this story," so it probably didn't impact the movie's awards season prospects.

But he added: "The controversy over Lyndon Johnson in 'Selma' may have hurt that film.

"They can tinker with facts but you need to know who's the hero and who's the villain."

Oscars voters don't like it when a character's historical role or personality is transformed from one to the other, he said.

But Nunan said that some playing with the facts -- though not too much -- was inevitable.

"A motion picture has to take some liberties, otherwise it won't win the viewers emotionally," he said.