LONDON, ENGLAND - User photographs can still be found on many social networking sites including Facebook after people have deleted them, British researchers said Thursday.

The findings by a team from Cambridge University raise questions about the ability of users of the sites to permanently delete potentially embarrassing photographs.

The researchers posted photographs on 16 popular websites and noted the web addresses where the images were stored, before deleting them.

But researchers said that although the images appeared to have gone, they were still able to find them 30 days later on seven sites, including Facebook, by using the direct web addresses.

Special photo-sharing sites, such as Flickr and Google's Picasa, fared better than Facebook and Microsoft's Windows Live Spaces removed the photos instantly, the research found.

Joseph Bonneau, an American member of the research team, told AFP: "When you delete a photo, many of the sites don't actively remove it, they basically just wait for it be overwritten.

"In theory, the photos could take months to disappear.

"It is possible to have them removed right away but it takes more work on their part so it is easier for them just to leave it.

"They have a responsibility to ensure users' privacy and they are not fulfilling that responsibility."

A spokesman for Facebook said that while photographs are deleted from the site immediately, they may continue to exist for a short time elsewhere.

"When a user deletes a photograph from Facebook it is removed from our servers immediately," the spokesman told the BBC.

"However, URLs to photographs may continue to exist on the Content Delivery Network (CDN) after users delete them from Facebook, until they are overwritten.

"Overwriting usually happens after a short period of time."