Somehow the word got out. Doppelgänger Week had arrived. What a great idea. Change your Facebook profile picture to a photograph of someone famous to whom you have been likened in the past. I'm not sure if it was the personal touch or the pure simplicity of the concept, but it quickly caught on. Presumably possessed by the otherwordly momentum building up behind the fad, SHN tweeted feverishly on Monday, "So it's Doppelgänger Week on Facebook. SHN will have a write-up before you can say lookalike!" Well, I decided to wait things out. I took a moment to collect my thoughts, change my own profile picture to a wistful shot of the Milky-Bar Kid and watched the trend develop.

Thing is, of course, the basic activity isn't very interesting at all. People look alike sometimes. Well, we're the same species. Go figure. But what is weird (darn-tootin' spooky, if you ask me) is that Doppelgänger Week seems to have come to us out of the ether. A debate has been raging on many a blog since the weekend over the origins of the idea. Either someone is telling fibs, two (or three) people thought of the same idea at once, or Facebook has been the subject of what could only be described as a (somewhat benign) paranormal influence.

First of all, the Huffington Post interviewed someone called Bob Patel - a 19-year-old who claimed the idea for his own. He allegedly got the idea after he was ridiculed in work for being the spitting image of Tom Selleck. "I.T. is a notoriously ruthless department" he remarked. To make matters worse, HuffPost didn't see the likeness and the interview retains a sceptical tone about Patel's authorship of the fad, and its merits in general.

The NowPublic social media blog got involved after writing about the phenomenon and being approached by another D-Week claimant, Chloë Carter. NowPublic has since put together an account of the various individuals who say that they inspired Doppelgänging (that isn't a word). Carter purportedly expressed her indignation that Facebook users were creating Doppelgänger groups in an attempt to steal her limelight. Here are one and two examples of such usurpation. She was out to put the record straight. Hell, if you're gonna fight, you've got to have something worth fighting for, no?

Carter and Patel have been the most vocal claimants, but the number of supposed architects of the trivial scheme has now reached the absurd. People have been so taken by the idea that they have posted desperate queries on Q&A websites in the hope of discovering the truth. There's clearly a lot of kudos associated with D-Week. The face-recognition application at MyHeritage.com claims that it is "powering Doppelgänger week and handling millions of photos every day." It's still uploading mine.

Well, today (GMT) marks the official end of D-Week. It's been quite an experience for reasons which border on the surreal. Thanks web 2.0! It has to be said that some of the eccentric blogging and tweeting the craze has brought us will be sorely missed. (Try this example which addresses the solemnly-posed question: "What if no one told me I look like anyone famous?") There were even one or two entertaining (and inexplicable) YouTube contributions to enjoy. Like the one below. (Watch till the end.)