This was first brought to my attention in the 1970s, when a neighbour was showing us some of the candid slides he used to take of people. When a close-up appeared of the face of a man he snapped in a park, I immediately exclaimed: "I know that man! He attends my German class at University."
So, having borrowed the slide, I took it to my next class. "That's Mr. X," said the first person who saw it. "No, it isn't," opined another woman. "His earlobes are different."
I held it up to the light, at the same time gazing at Mr. X. Yes, the earlobes were different. But everything else was identical. And how many people look closely at earlobes? It was a good thing he hadn't been in a police lineup. He'd have been hanged on my testimony.
At that, he stepped out again, and we took no notice. It didn't occur to us that he was going to So-and-so's room. But a few minutes later, he returned, bearing the large, glossy Daily Mirror nude calendar. "Oh, Helen!" said one of the girls, "you've grown!" - for the model was slightly more buxom than Helen. She appeared a little embarrassed as we insisted she stand next to the photo, which was at least half natural size. There was no doubt about it: from the shoulders up, the two were identical. Even their earlobes were the same. I tell you, if it hadn't been for the fact that the model was somewhat better developed below the shoulders, we would have assumed that shy, religious Helen had been moonlighting as a nude model.
Having a double can be tricky. My Texan brother-in-law once had a gun held to his head by a law enforcement agent. His name is Tim, and he bore more than a passing resemblance to Tim McVeigh, the Oklahoma bomber. Also, I think it was in the 1980s that a journalist from Sydney flew out to Brisbane to attend the Brisbane branch of his newspaper chain. Hardly had he got off the plane, than a policeman demanded to know who he was and what he was doing there. This happened a couple more times before he arrived at the office, and he was starting to wonder what sort of perverse spirit was animating the Queensland police. Of course, once he reached the office, his colleagues showed him a story they had been running about an escaped prisoner doing time for rape and - guess what! - he bore more than a passing resemblance to the journalist.
Of course, for Richard Jones it was even worse. He spent 17 years in prison for a crime his double committed.
My own number finally came up eight or ten years ago. I had just stepped into a lift when a man cried, "Good day, Greg!" He said it again, and eventually I realized he was talking to me, so I told him my real name. "Well, I'll be!" he replied. "You're the splitting image of Greg Y!"
Well, that was a relief. I was always afraid I would one day be accosted by a wronged husband, a loan shark, or some underworld figure. At least now I know my double had been behaving himself.
And Greg, if you're reading this, I've been behaving myself too.
Up-date: Since posting this, a report has come in of two young women who are almost the splitting image of each other, even though they are are unrelated strangers. You can read it here.
In fact, it appears there were three duplicates, and some other people found their doppelgängers. Check it all out on Twin Strangers.
Up-date 2021. I finally got around to reading The Prisoner of Zenda, and found it a thoroughly entertaining tale about a man, Rudolf Rassendyll, who is the splitting image of the imprisoned King of Ruritania. However, when it came to the coronation scene, the thought occurred to me: he may look like the King, but he can't possibly sound like the King. Although he speaks fluent German, he is an Englishman, and Ruritania would have its own accent, even its own dialect. Even if Rassendyll were a native Ruritanian, his voice would be different from the King's. This does not, of course, mean that he could not pull it off. Imposture by a double, especially of a king, is such an extraordinarily rare event that no-one would even suspect it. Nevertheless, one would expect the King's intimates (Rassendyll even romanced the King's fiancée) to at least comment on it. This is a weakness in all such stories.
I shall now have to reread The Prince and the Pauper to see how Mark Twain dealt with the problem. From memory, I don't think he did.