A senior US military official confirmed that the video - released by whistle-blower website WikiLeaks.org - was authentic.
Reuters has been pressing for the release of the video, which consists of 17 minutes of black-and-white aerial video and conversations between pilots in two Apache helicopters as they open fire on people in Baghdad.
Twelve people died in the attack, among them Reuters photographer Namir Noor-Eldeen, 22, and driver Saeed Chmagh, 40.
WikiLeaks said it had acquired the video from whistle-blowers in the military and was able to view it after breaking the encryption code.
David Schlesinger, the editor in chief of Reuters news, said in a statement that the video was ''graphic evidence of the dangers involved in war journalism and the tragedies that can result''.
On the day of the attack, US military officials in Baghdad said that the helicopters had been called in to help US troops who had come under fire during a raid. But the video does not show hostile action. Instead, it begins with a group of people milling around on a street, among them, according to WikiLeaks, Noor-Eldeen and Chmagh. The pilots believe them to be insurgents, and mistake Noor-Eldeen's camera for a weapon. They aim and fire.
''Look at those dead bastards,'' one pilot says. ''Nice,'' the other responds.
A US military investigation concluded that the forces involved had no reason to know that there were Reuters employees in the group. No disciplinary action was taken.
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