2 July 2012
University at Albany computer scientist Siwei Lyu and colleagues have identified a method of using “noise” to authenticate digital photography.
By using statistical and computational analysis, Lyu’s team developed techniques that measure noise strength across a photo to determine which parts of the photo originated from different sources. Lyu says the method is advantageous in that it does not explicitly rely on the knowledge of the image format, camera model, or tampering procedure, and has a high level of detection accuracy.
Noise, the digital equivalent of film grain, exists in all digital photography, and is generally invisible to the human eye. Numerous factors during and after a photo is taken introduce noise, such as temperature and thermal conditions, sensor saturation, quantization, compression, and transmission. An unaltered image is expected to have uniform noise strength across all pixels, but inconsistencies in noise variances in altered photos become telltale evidence of tampering.
“Collectively, the digital image forensic community aims to provide a series of tools that can significantly limit the extent of undetectable manipulations, or increase the real cost, in terms of time and technical sophistication, of making a believable forgery,” Lyu says.
Communications of the ACM