Articles

Detecting Altered Images

Alexey Kuznetsov, Yakov Severyukhin, Oleg Afonin, Yuri Gubanov © Belkasoft Research

Summary

Are digital images submitted as court evidence genuine or have the pictures been altered or modified? We developed a range of algorithms performing automated authenticity analysis of JPEG images, and implemented them into a commercially available forensic tool. The tool produces a concise estimate of the image’s authenticity, and clearly displays the probability of the image being forged. This paper discusses methods, tools and approaches used to detect the various signs of manipulation with digital images.

How many kittens are sitting on the street? If you thought “four”, read along to find out!

Introduction

Today, almost everyone has a digital camera. Literally billions of digital images were taken. Some of these images are used for purposes other than family photo albums or Web site decoration.

On the rise of digital photography, manufacturers of graphic editing tools quickly catch up momentum. The tools are becoming cheaper and easier to use – so easy in fact that anyone can use them to enhance their images. Editing or post-processing, if done properly, can greatly enhance the appearance of the picture, increase its impact to the viewer and better convey the artist’s message. But where is the point when a documentary photograph becomes fictional work of art?

While for most purposes editing pictures is more than okay, certain types of photographs are never to be manipulated. Digital pictures are routinely handed to news editors as part of event coverage. Digital pictures are presented to courts as evidence. For news coverage, certain types of alterations or modifications (such as cropping, straightening verticals, adjusting colors and gamma etc.) may or may not be acceptable. Images presented as court evidence must not be manipulated in any way; otherwise they lose credibility as acceptable evidence.

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