Jackie Bernstein of Natomas is Kelly Clarkson.

Kayla Moreland is Alicia Silverstone.

Michael Stockinger is Jesus – because when he was at Sacramento State he had long hair, a beard and always wore flip-flops.

Since late last week, Facebook users have been swapping their profile pictures for their celebrity look-alikes.

They've been participating in "Doppelgänger Week," the current Facebook trend, which follows last month's "What Color is Your Bra?" meme. And flows into "Urban Dictionary Week," prompting Facebook users to look up their names and post the definition.

As the social network grows – in December, according to several Web site trackers, Facebook logged 100 million-plus unique visitors – its trends, while not new, recently have taken on an expansive organized quality.

"People are endlessly fascinating, and Facebook is a platform for people," said BJ Fogg, director of Stanford's Persuasive Technology lab, who teaches courses about Facebook. "People naturally watch what other people are doing and copy it."

For Doppelgänger Week, users become someone else in cyberspace, from Angelina Jolie to Cookie Monster.

"One of my friends put up Glenn Beck's photo and I immediately burst out laughing because it's so true," said Moreland, 22, of Carmichael, who is Silverstone this week.

Last week, status updates on the site read: "It's Doppelgänger Week on Facebook; change your profile picture to someone famous (actor, musician, athlete, etc.) you have been told you look like."

Facebook participants are using the term "week" loosely. The consensus from users seems to be it ends on Sunday.

Like many viral Internet trends, Doppelgänger Week started simply with an idea that is flattering (what celebrity do you look like?), conversation-provoking (you do/ don't look like him/her) and easy (post a picture). An average Joe named Bob Patel said he was the brainchild.

Patel told the Huffington Post his co-workers teased him about being the Indian version of Tom Selleck.

"They're like, 'Hey, Tom Selleck, what are you doing?' Or, 'Yo, Tom Selleck, we're talking to you. …' In any case, that's when I decided to turn the joke around on them and came up with Doppelgänger Week," he said.

Users started changing profile pictures, prompting friends to change theirs, too.

At his friends' urging, Kevin Eastman, 28, of Sacramento posted a photo of Steve McQueen.

"Considering McQueen died in '80 and Eastman was born in '81, I would even go so far as to argue that Kevin is – in fact – the reincarnation of McQueen," said his friend, Colin Sueyres.

Eastman, a state Assembly staffer, is less sure.

"I've been hearing it for years, but I don't know if I entirely agree," he said.

Richard Crawford, 42, is a Web developer for UC Davis, and he chose Emperor Norton, a 19th-century eccentric San Franciscan. Crawford felt the connection, beyond his habit of occasionally dressing in Victorian-era clothing.

"We not only look alike because we're not very tall, have dark hair and a beard, but I think I share his idealism and optimism," said Crawford. "He was also kind of crazy."

Other sites have benefited from traffic. Ancestry Web site Myheritage.com has declared itself the "unofficial supplier." The Israel-based company has a free "Celebrity Toolbar" program that enables users to match their uploaded photos with celebrities.

The Celebrity Toolbar relies on facial recognition technology originally developed to help discover ancestors based on facial similarity.

The company's servers broke down because so many people tried to access the Celebrity Toolbar, a company spokeswoman said.

Facebook also benefits indirectly, said Fogg, the Stanford professor. "It makes Facebook more fun, and any time that happens the company becomes richer," he said.

While posting celebrity photos is technically a violation of the Facebook terms of service, the company said it won't ask users to remove any Doppelgänger Week photos unless it receives complaints.

Fogg said he suspects Doppelgänger Week took off because the idea was fresh yet did not require users to learn a new task.

"It's not asking you to record an audio snippet or anything," he said. "It's just finding a photo and uploading it, and it fits into the culture and activities that already exist on Facebook."

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