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: Computerized emotion detector

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

Computerized emotion detector

Sep 16, 2014

Face recognition software measures various parameters in a mug shot, such as the distance between the person's eyes, the height from lip to top of their nose and various other metrics and then compares it with photos of people ...

Cutting the cloud computing carbon cost

Sep 12, 2014

Cloud computing involves displacing data storage and processing from the user's computer on to remote servers. It can provide users with more storage space and computing power that they can then access from anywhere in the ...

Teaching computers the nuances of human conversation

Sep 12, 2014

Computer scientists have successfully developed programs to recognize spoken language, as in automated phone systems that respond to voice prompts and voice-activated assistants like Apple's Siri.

Mapping the connections between diverse sets of data

Sep 12, 2014

What is a map? Most often, it's a visual tool used to demonstrate the relationship between multiple places in geographic space. They're useful because you can look at one and very quickly pick up on the general ...

User comments : 0