IT’S HAPPENED TO the best of us. We purchase a shirt, a pair of shoes, a hat that we love and think is totally unique—and then show up at school or work and see someone wearing the exact same thing. It’s a little embarrassing. Hans Eijkelboom takes that feeling to another level with People of the Twenty-First Century, a photo series that suggests we’re more like sheep than snowflakes.

Eijkelboom has spent more than 20 years photographing people out and about in similar clothing. Though humorous, he isn’t poking fun at anyone. Instead, he uses the series to highlight how similar our tastes and styles have become in the modern world.

“For me it’s not about the fashion, but more about our identity,” says Eijkelboom. “I’m showing that sometimes it is nearly impossible to not go with the flow.”

He made the first photos in 1992 in Arnhem, Holland where he was living at the time. The photographer has since shot in Paris, New York, and Amsterdam to name a few, amassing some 6,000 images of collective sameness for his photo book. Eijkelboom is always looking for a busy shopping center or noisy street corner —anywhere there may be a crowd. Once he’s got a spot, he spends 10 or 15 minutes observing what people are wearing and photographs whatever he sees most often—be it plaid shirts, denim skirts or murses. He tries to spend no more than two hours shooting—a timeframe that he says helps his eyes stay fresh.

Eijkelboom wears his camera—usually a 35mm—on a strap around his chest but doesn’t peer through the viewfinder. Instead he fires remotely with a trigger so his subjects are more candid. The result is a visual catalog of seemingly mindless “individuals” who are moments away from passing their twin … or twins, depending on how long you wait.

Traveling around the world, Eijkelboom says there was a time when New York was the most vibrant place to shoot. Nowadays, Tokyo is probably his favorite location because “the relationship between identity and clothing is very big there.” In the future he’d like to work in places like Istanbul, not only because it’s a cosmopolitan city, but because it’s a place of distinctive religions and histories that can have a huge impact on identity.

The photographer is now 65 and living in Amsterdam, still working on his project. He feels there’s a shift in identity as society transitions from what he calls an analog world to a digital one. With the Internet and social media defining a lot of how we present ourselves, Eijkelboom believes people are less concerned about expressing themselves through clothing.

“I cannot predict the future, but I am sure that in 10 or 15 years we will all be a different kind of human being,” he says. “We are just at the beginning of this change to the digital world.”