Concert halls, art museums, gym locker rooms and other public places where photography is greatly discouraged may have problems from another device – cell phones.

Cell phones with attachable cameras or cameras embedded in them have become so ubiquitous in Hong Kong, for example, that gyms there are prohibiting people from making calls in the locker room.

"Some of these phones can be used as cameras," Miran Chan, a spokeswoman for the Physical chain of gyms, told CNN last month. "If someone uses a phone this way and takes a photo and puts it on the Internet, it's not very good for our members and their privacy."

What's alarming to some health enthusiasts is how popular, widespread – and clandestine – these phones are.

In Britain, for example, BBC News Online accepts public submissions of photos taken on camera phones.

Global sales of mobile phones that can take, send and receive pictures rose 65 percent in the last quarter from 5.2 million units to 8.6 million phones sold, according to market research firm Strategy Analytics. These numbers do not include snap-on cameras that could be purchased for as little as $100 for the phones.

Asia accounted for 80 percent of total camera-phone sales in the fourth quarter of last year, while Western Europe snagged 13 percent of the phone-camera market. Both North America and Eastern Europe claimed 2.3 percent of total camera-phone sales each in the same period of time.

Despite any privacy concerns that may have arisen from the incident in Hong Kong – one U.S. cell-phone carrier called it "an aberration" – cell-phone companies are heavily marketing the handsets to both consumers and businesses.

While consumers tend to use the devices to take pictures of their families and friends, businesses also see the value in the phone. Sprint PCS spokesman Dan Wilinsky used the example of the insurance adjuster who takes a quick snapshot at the scene of an accident and instantly sends it back to the office.

"With the color screens of the phone, (camera phones) are more and more in demand," Wilinsky said. "You will see more and more in weeks and months to come."

Cell-phone manufacturers Nokia and Sony-Ericsson said that the camera phone did not have any more potential for misuse than any other digital camera, which nowadays can be as small as a pencil or a credit card, Nokia spokesman Keith Nowak said.

"You'd have to be pretty good not to tell someone you are taking their picture," Nowak said.

To take a picture on a camera phone, the user must point and click the phone at the subject. While most of the phones do not have flashes on them, they do make a shutter noise to alert the user that the picture has been taken, Nowak said.

While the pictures may appear somewhat fuzzy on the low-resolution screen of a phone, they can appear vivid over the Internet, admits Sony-Ericsson spokeswoman Nicky Csellak-Claeys. That's what's got some gym-goers, even in the United States, a little worried.

"Well, yeah," said Michelle Guglielmo, a 25-year-old sales representative who was recently at a 24 Hour Fitness gym in San Francisco. "You're naked. You're exposed. It's not a nice thing to think about."

All 24 Hour Fitness clubs post signs saying, "No filming, videotaping or photography is permitted in the club without the written permission of management," a company spokesman said.

"The new camera-cell-phone combinations are no exception to this rule," he said.

The Gold's Gym in Oakland, California, also said it hasn't witnessed any clandestine picture-taking there. "If it does, we will deal with it when it comes," said Gold's Gym manager Chris Davies.

But one group of people that privacy advocates and industry analysts expect to hear from in the upcoming months are copyright holders such as museum exhibitors and concert musicians.

Not many artists made a fuss over file trading when people were relying on dial-up connections to download music, said Cedric Laurant, policy counsel for the Electronic Privacy Information Center in Washington. Fast-forward to today's broadband era and music-swapping sites are being sued left and right by copyright holders because it is so quick and easy to download a song, he said.

"If someone is able to take a picture of a show, then simulate the picture on the Internet – it may very well constitute an infringement to copyright laws," Laurant said. "The owner of the premises might well consider a ban on the cell phone, depending on what he considers most important – the patron's right to use the cell phone on the premises or the interests of intellectual property owners."

As the quality of the images improve and the phones become more pervasive – some Asian markets claim upwards of 30 percent camera-phone users, said Seamus McAteer, analyst for Zelos Group – more discussion and even public bans of the phone will arise, he said.

"The clandestine camera is a hornet's nest for potential social issues," McAteer said.

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