Scientist finds telltale noise in altered photos

Jun 26, 2012
At left, doctored photo of Tiger Woods and a flamingo as a golf club; at right, the exposing of differences in noise variance between Woods (low) and flamingo (high) elements.

(Phys.org) -- University at Albany Computer Scientist Siwei Lyu and colleagues, working in partnership with the New York State Center for Information Forensics and Assurance (CIFA), have identified a new method using “noise” to authenticate digital photography. The research is supported by a grant from the National Science Foundation (NSF).

The team presented its findings for exposing splicing by measuring "noise" levels discerning discrepancies in photos at the IEEE International Conference on Computational Photography.

"Whenever a photo is manipulated digitally, the underlying characteristics of the image pixels are disturbed in a way that they become unnatural,” Lyu explains. “Though human eyes may not be able to detect such subtle changes, they can be readily picked up by computer algorithms. The techniques developed aim to make sure that more significant manipulations can be detected."

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. While an unaltered image is expected to have uniform noise strength across all pixels, inconsistencies in noise variances in altered photos become telltale evidence of tampering.

Using statistical and computational analysis, Lyu's team developed techniques that effectively measure strength across a photo to determine which parts of the photo originated from different sources.

According to Lyu, the method is advantageous in that it does not explicitly rely on the knowledge of image format, camera model, or tampering procedure, and has a high level of detection accuracy.

The past decade has witnessed significant advances in digital image processing and computational photography, resulting in sophisticated image-editing software systems such as Adobe Photoshop and GNU Image Manipulation Program. Yet the ease of digital image manipulation has also posed new challenges, with digital images becoming more vulnerable than their non-digital counterparts to malicious tampering.

"Collectively," Lyu said, "the digital image 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."

Explore further: Coping with floods—of water and data

More information: www.albany.edu/main/lyu-iccp.shtml , research.microsoft.com/en-us/u… ond/events/iccp2012/

add to favorites email to friend print save as pdf

Related Stories

Investigating Digital Images; What's real and what's phony?

Jul 01, 2004

''Seeing is no longer believing. Actually, what you see is largely irrelevant,'' says Dartmouth Professor Hany Farid. He is referring to the digital images that appear everywhere: in newspapers, on Web sites, in advertising, ...

Reversible watermarking for digital images

Jul 06, 2010

Every picture tells a story, but how do you know that a digital photo has not been manipulated to change the tale being told? A new approach to adding an encrypted watermark to digital images allows the an image to be validated ...

Recommended for you

Coping with floods—of water and data

4 hours ago

Halloween 2013 brought real terror to an Austin, Texas, neighborhood, when a flash flood killed four residents and damaged roughly 1,200 homes. Following torrential rains, Onion Creek swept over its banks and inundated the ...

Cloud computing helps make sense of cloud forests

Dec 17, 2014

The forests that surround Campos do Jordao are among the foggiest places on Earth. With a canopy shrouded in mist much of time, these are the renowned cloud forests of the Brazilian state of São Paulo. It is here that researchers ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.