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updated 4/9/2013 7:49:47 PM ET 2013-04-09T23:49:47

Storing racy photos using cloud storage can be risky. Customers of the image-hosting service Photobucket learned their lesson the hard way last year when hackers plucked nude photos from the site and posted them in a public forum. And with today's facial recognition technology and vast public databases like Google Images, it's not difficult to put a name with a face.

But researchers at USC have come up with a new tool to thwart those who would expose private photos.

Engineering professors Antonio Ortega and Ramesh Govindan teamed with USC Ph.D. student Moo-Ryong Ra to design and test a two-part system called P3 (Privacy-Preserving Photo Sharing). P3 uses partial encryption that allows users to share photos and to control who can see them. To date, the program works with Facebook and Flickr, but could easily be adapted for other networks, such as Instagram, according to the team. [See also:  Private Porn Pics Aren't Private for Long

How it works

P3 splits a photo into two parts: a public part, which contains most of the original and is uploaded to a website, and a secret part that contains most of the original’s information but is stored separately from the photo-sharing site. Only when viewers are given access by the photo's owner to the "secret" part can the photo be seen; otherwise, the image appears as a gray box.

While photo  encryption  programs are available, most sites block them because the programs prevent sites from scaling images to fit designated formats; the programs also prevent them from resizing photos to fit different sizes of device screens.

P3 also provides security for photographers who are concerned about a website using photos without compensating them.

"Nobody doubts the convenience of cloud-based sharing; the question is whether we can trust third parties to protect our photos from unauthorized distribution or use," Ortega said in a statement. 

Who controls user content?

Instagram faced an uproar late last year when celebrities left the photo-sharing site, fearing that  Instagram's new service terms  would allow it to use photos for advertising. While Instagram assured users it would not use their photos, terms of service for most social media sites leave the door open to accessing user content without permission.

"Facebook still retains the rights to the portion of the photo that you've uploaded — but that portion is a degraded, unrecognizable mess," Ortega said. "Only you retain the rights to the complete photo."

The P3 technology has been granted a provisional patent and the research team plans to launch a company this summer to market it to the public. They suggested that  photo-sharing  sites could offer P3 as a paid service to users.

Follow Leslie Meredith  @lesliemeredith. Follow us  @TechNewsDaily, on  Facebook  or on  Google+.

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