Why do you put pictures?

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The cyberworld is technically a different place where people exist. It's like a different dimension of life on earth, a different domain. Although, in the cyberworld real people exist, why do some of them put picture in the avatar which definitely is not theirs? Like a picture of real person, say an actor or a celebrity. Is it because they want to be associated with them or are they like, pretending that he is what he's not? Or just to get more traffic and response perhaps? Why? Tell me?