Virtual possessions -- digital imagery, Facebook updates, online music collections, e-mail threads -- have a powerful hold on teenagers, U.S. researchers say.

Researchers at Carnegie Mellon University say the very fact that virtual possessions are without physical form may actually enhance their value, a university release reported Monday.

"A digital photo is valuable because it is a photo but also because it can be shared and people can comment on it," said John Zimmerman, associate professor of human-computer interaction and design.

For the 21 teenagers in the CMU study, a digital photo that friends have tagged, linked and annotated was more meaningful than a photo in a frame or a drawer, the researchers found.

One study subject said she takes photos at events and uploads them immediately so she and her friends can tag and talk about them.

"It feels like a more authentic representation of the event," the 16-year-old told the researchers. "We comment and agree on everything together … then there's a shared sense of what happened."

Those in the study said they could display things online, such as a photograph of a boyfriend disliked by parents, which were important to their identity but could never be displayed in a bedroom.

In fact, the teenagers said, the online world allowed them to present different facets of themselves to appropriate groups of friends or to family.