Multimedia Forensics
Multimedia Forensics
  • Kim Hyoung Joong Professor at Korea University (kh
  • 승인 2011.04.21 09:31
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Hyoung Joong Kim received his PhD at Seoul National University. His main research topics include data hiding and statistical detection, multimedia forensics, machine learning, and virtual economy. He is currently a core partner of the 3DLife (EU FP7 project), and Head of the Smart Media Association.

Pictures do not always reveal the truth: people like to manipulate photographs as long as they can. Now the work is done more mechanically and many new cameras even allow the people in the picture to automatically look prettier and slimmer.

For historians, however, a very old photograph, even with a torn edge or discoloration, can become a precious and unique clue to a historical fact just like a fossil.

From that point of view, pictures are honest - even though not perfectly so. Although the major part of them may remain as they should be, parts of it could have been adjusted to desired effects.

When the media stopped reporting on Kim Jong-il, different kinds of rumors began to spread: some people suspected he is suffering from some kind of serious illness and others believed he might be already dead. And as soon as his picture appeared on newspapers again, skeptics said it could have been fabricated. Some even went on to argue that it was a fake photo designed to hide Kim's death from the rest of the world.

The media, then, employed all kinds of traditional methods to determine the authenticity of the picture, by studying the shadow, highlight, vanishing point, edges, and texture.

The photograph eventually ended up in the hands of Hany Farid, a professor at Dartmouth College and one of the top specialists in the field, but the quality of the original picture turned out too poor to lead to any scientific conclusion. Extracted from newspaper or television, the pictures were of such low resolution that technical analysis was practically impossible.

Today, photographs are widely used as evidence in court. To that end, multimedia forensics has made a huge contribution to determining the truth or falsehood, or the extent of the truth of an allegation.

Late in 2010, a reporter from a current affairs TV series came to show two pictures, one of which he suspected was fabricated, and asked me to find out the truth. Apparently, he already possessed a few pieces of evidence to support the alleged fabrication of one of the photographs. The evidence provided by experts consisted of analyses on vanishing points, shadows and other attributes I mentioned earlier.

Both photographs were submitted as evidence to the court. While the plaintiff's picture was clear, the photo that the defendant supplied not only had low resolution, but it also contained the buildings that were tilted at a suspiciously peculiar angle.

After setting up a 3D model based on the two photos and Google Maps, I found out the likely location where the picture was taken, and then proved the plaintiff wrong. Part of the plaintiff's claim was merely a result of an optical illusion.

So I suggested they remove the allegation that the defendant's photograph was manipulated, and also said that they should seek confirmation from the 3D model experts. Eventually, that part of the show was not broadcast and I helped to prevent giving misinformation to the public.

Farid recently examined the photograph of Lee Oswald, the supposed assassin of John F. Kennedy. Some historians argued that the picture was forged, pointing at the seemingly unnatural shadow cast under his face. However, Farid's 3D model constructed using the mug shot and profile picture taken after Oswald's arrest showed that the historians' argument was also based on optical illusion. This case simply illustrated how dangerous it can be to analyze photographs with only the naked-eye.

Photo analysis requires special technologies such as signal processing and simulation. Even for a trained expert, it is not easy to determine with bare eyes whether a photograph was, for example, stretched, an adjustment often made when making a montage.

Nonetheless, Farid developed a technique by which it is possible to detect the direction and proportion of even minor stretches; while my own invention allows recognition of interpolation methods. But such research is still in the embryonic stage of development with manifold challenges and insufficient number of experts at the moment.

A photograph can bring justice or injustice to someone's life, which is why it is crucial to be able to accurately analyze and extract facts from it. With widespread digital cameras, people will not only take more pictures, but also be able to easily forge the pictures using rapidly improving digital editing tools. And consequently, the utility and necessity of photo analysis will increase, although it is not simple to find out who took those pictures when and where as well as what camera was used and whether and how it was altered.

It is not just a photograph. The same holds true for audio and video. Digital information can be delicately manipulated. However, a minute trace left unnoticed will allow scientists get closer to the truth.

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