They've no idea what to make of the strange people who have appeared on the far riverbank, wearing clothes, carrying cameras, and using alien transportation devices. But they are right to be concerned.
The people captured in the photograph belong to the Mascho-Piro, one of the world's last uncontacted tribes. For a millenium, they have carved an existence from the Peruvian rainforest, untouched by what outsiders call civilisation.
Now their days of isolation seem numbered. Illegal loggers are encroaching nearer to their ancestral homeland, in and around Manu National Park in the largely unexplored region where Peru borders Brazil and Bolivia.
The family were chanced upon by Diego Cortijo, an indigenous Peruvian exploring the Alto Madre de Dios River four days on foot from the remote jungle town of Puerto Maldonado.
Holding his camera lens against a telescope, he captured one of the most detailed pictures of an uncontacted tribe ever taken. It appears to show a family gazing at him with a mixture of fear and hostility.
A second image was taken by Gabriella Gali, an Italian visitor on a bird-watching tour of the national park.
She was taking a speedboat down the Alto Madre de Dios, a tributary of the Amazon, when she spotted humans on the far bank. Concerned a tourist could come so close to uncontacted tribes, Gali passed her photograph to Survival International, which fights for the protection of indigenous people.
The British-based group provided the photos exactly a year after releasing aerial photos from Brazil of another tribe classified as uncontacted, one of about 100 such groups it says exist around the world.
So-called "first contact" with the outside world can prove fatal for a tribe and usually results in the death of between 50 and 80 per cent of its members, who have no immunity to diseases common elsewhere.
It can also be tragic for those who "discover" them. Weeks ago, a close friend of Cortijo - Nicols "Shaco" Flores - was killed by an arrow on the outskirts of the park while trying to leave gifts of food and clothes.
"Shaco's death is a tragedy: he was a kind, courageous and knowledgeable man," wrote anthropologist Glen Shephard, a friend of the victim, on his blog. "Yet in this tragic incident, the Mashco-Piro have again expressed their adamant desire to be left alone."
Flores could communicate with the Mashco-Piro because he spoke two related dialects, said Cortijo, who added that Flores had previously provided clan members with machetes and cooking pots.
The Mashco-Piro tribe is believed to number in the hundreds and lives in the Manu National Park. .
Although it's not known what provoked the Mashco-Piro clan to leave the relative safety of their tribe's jungle home, Beatriz Huerta, an anthropologist who works with Peru's agency for indigenous affairs, speculated their habitat is becoming increasingly less isolated.
The upper Madre de Dios region where the tribe lives has been affected by logging, she said.
Huerta said that naturalists in the area and Manu National Park officials told her during a recent visit that a rise in air traffic related to natural gas and oil exploration in the region is adversely affecting native hunting grounds, forcing increasing migration by nomadic tribes.
The clan that showed up at the river is believed to number about 60, including some 25 adults, said Professor Carlos Soria of Lima's Catholic University who ran Peru's park protection agency last year.
The Mashco-Piro live by their own social code, which Soria said includes the practice of kidnapping other tribes' women and children.
He said the Mashco-Piro are one of about 15 "uncontacted" tribes in Peru that together are estimated to number between 12,000 and 15,000 people living in jungles east of the Andes.
- Independent, AP