Holograms keep paparazzi on their toes
Scientists have developed a new way of detecting whether celebrity photos are the real thing.
The technique, which uses computer generated holograms, could also be used to prevent hackers from tampering with sensitive legal images including fingerprint records and medical scans used as evidence in court.
The technique works by adding an invisible 'watermark', like a company logo, to a digital photograph, either by the camera when the picture is taken or afterwards.
If, for instance, an unscrupulous picture agency tries to alter a photograph to make it more newsworthy before selling it to a magazine or newspaper, the watermark is damaged.
The publication buying that image will then be able to detect this damage using special software.
Before the watermark is added to the photograph, it is turned into a computer generated hologram.
This is, in effect, a simulation of the pattern of light waves recorded when a real hologram is made.
Like all holograms, a small part of the computer generated hologram contains enough information to recreate the entire image, in this case the watermark.
So even if the watermark is damaged as the photograph is digitally manipulated, people can still trace the originator of the primary image.
Australian researcher Professor Claude Roux, director of the Centre for Forensic Science at the University of Technology Sydney, believes the main advantage of this technology is not that it detects digital fraud; a number of techniques already do that.
He says the technique makes it possible to identify where the primary image came from, which will be useful for verifying the image.
But as with many techniques developed for detecting forged images, he says there are still issues of security.
The watermark is encrypted before adding it to the image, so that only those who know the private key or unscrambling code can reconstruct it.
Roux asks what is to stop people getting their hands on this key or indeed 'cracking' the software and replacing the security with a watermark of their own?
"This technique is an interesting addition to the pool of methods applicable to authenticate digital images," he says.
"But this is definitely not a panacea. The best way to address this issue is by applying a holistic approach that includes, in addition to technical methods, strategies and frameworks that limit the opportunity to tamper, such as audit trails and best practice guidelines."