The time sequence was disclosed six weeks after the Al-Hillis, from Claygate, Surrey, were murdered close to Lake Annecy.
Eric Maillaud, the town's prosecutor, said it could be an insight into how and why they came to die on Sept 5.
Saad al-Hilli, 50, an engineer, his wife Iqbal, 47, and his 74-year-old Swedish mother-in-law, Suhaila Al-Allaf, were found dead in the family BMW. All were killed by semi-automatic gunfire, which also killed 45-year-old cyclist Sylvain Mollier, a French father who was hit by at least five bullets.
The Al-Hillis' four-year-old daughter, Zeena, survived the attack after hiding under her mother's corpse, while her sister, Zainab, seven, was badly injured.
Mr Maillaud said that a few minutes before their car had pulled up outside a house in the nearby village of Arnand, where they posed for the pictures.
Images retrieved in the BMW show "a real family photograph", said Mr Maillaud. "Both women were smiling and did not seem worried. This suggests that everyone was relaxed at the time."
But it is the timing of the pictures that is of particular interest to Mr Maillaud and two investigating French judges working with British detectives.
Brett Martin, 53, a veteran of the RAF, was the first to arrive at the scene on his bicycle. He has described how he gave first aid to Zainab, who had been shot in the shoulder and beaten around the head.
Mr Martin said he also checked the pulse of Mr Mollier, turned off the BMW's engine, and carried out a number of other tasks before realising his mobile phone did not have a signal. He then cycled down the hill and finally made a call to the emergency services logged at 15.48.
This would have meant a window of far less than 33 minutes for the killer – or killers – to end the lives of four people, attack a child, and disappear without trace through one of the most popular tourist regions in eastern France.
Detectives have been showing the photographs to villagers in the area but have refused to release them to the public because, said one police officer, they are considered "morbid".
Mr Maillaud renewed his appeal for the driver of a green 4x4 vehicle seen speeding towards the scene by Mr Martin to come forward, suggesting the car might have belonged to the national forestry office. Mr Maillaud added: "It's a theory but there is no certainty."
The prosecutor said there was particular interest in a bank account in the nearby Swiss city of Geneva in Al-Hilli's name. Believed to contain the equivalent of about £750,000, it is thought to be linked to a family will Al-Hilli was disputing with his brother, Zaid.
As well as the family feud, Mr Maillaud said the inquiry was concentrating on Al-Hilli's work on satellite systems, and his past life in Iraq, where he was born. The last photograph of the Al-Hilli family in Arnand is marked as having been taken at 15.15 on Sept 5.
Before the attack happened, the family would have had to get back in the car and drive to the outskirts of Chevaline.
Mr Mollier is reported by Mr Martin to have overtaken him before the attack, and would have reached the scene before him.
Mr Mollier was killed, but Mr Martin says he saw no suspects by the time he arrived, nor during the small amount of time between the photographs being taken and him calling the emergency services.