If you're one of Facebook's 350-million-plus members, you've probably noticed a handful of people on your friends list changing their profile photos to pictures of celebrities, cartoon characters, Muppets, and other notable figures recently.

That's because an unofficial viral craze called "Doppelganger Week" has arisen on the social network. To participate, you change your profile picture to a celebrity or otherwise notable figure whom you resemble (or like to think you resemble).

Nobody's really sure where Doppelganger Week came from or who started it. It's particularly funny considering the recent emergence of more photos from the set of "The Social Network," a movie based on the origins of Facebook in which the company's early executives are portrayed by, yes, celebrity doppelgangers.

The catch is, putting up a celebrity photo on your Facebook profile may not actually be kosher. In the company's terms of service, it says: "You will not post content or take any action on Facebook that infringes or violates someone else's rights or otherwise violates the law...We can remove any content or information you post on Facebook if we believe that it violates this Statement." So unless you took that celebrity photo yourself or bought the rights to it, it may be in violation.

More: http://news.cnet.com/8301-13577_3-10445698-36.html