(CBS) — Facial recognition can be explained this way: You see a face, and your brain tells you who you’re looking at.

But imagine being “face blind” — not being able to recognize the faces of people you know.

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CBS 2’s Ed Curran reports it’s a rare disorder that turns familiar faces into perfect strangers.

As a salesman, James Cooke picked out every face in the crowd.

“The first 49 years of my life I could walk into a room and just scan the room and know who I knew and who I didn’t know,” he says.

Now, He can’t even recognize a family member.

“I literally have walked right past my kids and not known it was them,” he says.

His son, Tommy Cooke, is mystified.

“I really didn’t understand at first. You know, ‘What do you mean you can’t recognize me? You’re my dad,’” he says.

Less than 3 percent of people have prosopagnosia, or face blindness.

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“If I close my eyes I cannot visualize even your face, and I’ve just been looking at you. I can’t visualize my husband’s face,” Beverly Feldt tells Curran.

She says she has developed other ways of recognizing people, including by hairstyle, glasses and clothing.

But Feldt adds: “Of course, those change, so that becomes very difficult sometimes.”

A brain injury or medical condition can cause it, as in James Cook’s case. But others, like Feldt, say they’ve always had it.

Dr. Jose Biller, a neurologist at Loyola University Health System, says face blindness is the inability to de-code the face you’re looking at.

“This is not a memory problem. It’s not a problem related to an impaired vision. It’s a brain disorder,” he says.

The degree of face blindness can vary. Dori Frame, who suffered a head injury as a teenager, is an extreme case.

“It’s your worst nightmare, walking into a room full of people who you know but can’t recognize,” she says.

She uses a service dog to identify friends and even her husband.

“All I have to do is say ‘find Greg,’ and he’s off like a shot through the crowd,” she says.

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There are tests to see if you may suffer from face blindness. For more information, click here.