Making it to the US in a photo finish

Exhausted but smiling, a migrant father with a young child strapped to his back gathers his family for a selfie to celebrate illegally crossing over the border into the US at Eagle Pass in Texas.

Behind him, a mass of hundreds of other asylum-seekers who had also made it alongside them Tuesday crush behind him, next to the border’s razor wire fencing.

The southwest border has been besieged, seeing upward of 10,000 people a day handing themselves over to officers for processing.

And there is no end in sight as the hordes keep coming, with Costa Rica declaring a state of emergency this week as migrants heading north have flooded over its borders.

Here, The Post brings a rare firsthand account of the journey the selfie-snapping dad and others made in the final push to cross the Rio Grande and reach the border through the eyes of an undercover photographer, whose name is not being revealed to protect their identity.

Photog’s chronicle:

The cameraman embedded with the caravan of migrants was led by the cartel’s people smugglers, known as coyotes.

He recalls: I joined the mostly Venezuelan group after they had worked their way up near the border by hiding on a freight chartered through Northern Mexico.

They had been battered by the wind and elements and, as the train had not stopped in many hours, had little chance to eat or drink.

As the sun set over the Rio Grande, we could see Eagle Pass, Texas, to the north. I was accompanied by a local who knows Piedras Negras, Mexico.

From the train tracks, it’s a hard 15 miles over rough terrain to the US-Mexico border for the migrants, who are all ages from elderly to toddlers. Some barely have shoes left, worn down from the hundreds of miles they have walked.

Once they got to the river, the smugglers were waiting. The migrants knew they would have to pay the cartel in order to be allowed to cross the river, as no one crosses without their permission.

Money changes hands but the transactions are done discreetly so it’s hard to say how much. The human traffickers were aware US journalists were documenting the crossing, but didn’t menace anyone and instead simply asked not to be photographed.

The smugglers separated everyone into groups of 50 to 100. They then staggered them, telling them exactly when to cross.

Everyone waited their turn, following the orders of the smugglers, one of whom acts as a guide, getting into the water and testing the route along the riverbed to make sure it’s crossable.

Once the migrants were in the freezing water, they were directed to hold onto a rope to help stabilize them.

Some were caught off guard as they entered the currents of rushing water and took a few uneasy steps trying to balance.

Most people held onto the rope for dear life where they could, and others held hands, hoping to stable themselves better during the crossing.

Many of those in the water were families — sometimes women with children traveling alone. Most parents put their kids on their shoulders to try and keep them out of the water completely.

Even among the adults, most were not strong swimmers or even used to the water.

One mom held her infant wrapped in a blanket close to her chest, with only the baby’s bald head visible near her face. One female toddler was placed inside an inflatable orange and lime green car for the crossing.

The smuggler guide went back and forth across the river multiple times helping his cargo — especially the elderly and children, cross. The water was very rough, especially for those holding babies and there was a lot of screaming.

We could hear the coyotes telling the migrants, “Don’t worry, this is nothing. Nothing is happening here.”