Can’t wait for Leeuwenhoek’s rebirth, how to scientifically identify fake photos with “no PS traces”?


People often say that hearing is fictitious and seeing is believing, but what if the photo is fake? There are many ways to identify fake photos-as long as you are careful enough. The picture below looks like two people are standing outside the building, one of them seems to be handing something to the other.

Take a closer look and you may find that the reality is not straightforward.

Piercing evidence is often hidden deep in the image, but for Hany Farid, the proof is dispersed in particular details, such as the direction of the light reflected by the windows and the misalignment of the shadows.

Research shows that most people are still very bad at identifying fake photos, no matter how bright we think we are. Farid, however, has special expertise as a specialist in the area of image processing. His careful research makes it hard to mask signs of difficult to detect tampering.

He has mastered a trick after years of practice, which is to observe the light in the eyes of people in photos. “He said:” We can see the reflection of the light source (such as the sun or flash) in their eyes when two people stand in the same image. The position, size and color of the reflected light tells us the light source ‘s position, size and color. If the two characteristics are inconsistent, this photo may be a composite.

The color of human ears may be a further flaw. When the sun is behind you, the front of the human ears appear red. This is because of dispersion. The redness of the ears will not be seen if the light comes from the front.

Yet there are more scientific arms in Farid. As the director of Dartmouth College’s computer science department, he has been learning how to recognize images that were processed decades earlier.

It is quick to recognise any false images, and the “Time” magazine at the Golf Club of the President is a false.

As an example , take the shadow. You will find the location of the light source if you draw a line from the edge of the shadow in the frame, leading to a point on the object that creates the shadow, by tracing this path. If you draw multiple such lines in the dark, at one point they can converge.

The shadows of certain objects in the photo do not match the source of light in the rest of the photo if the camera has been tampered with. Those images with elements inserted later can be defined by this process.

It shows such a fault in the previous shot. By drawing a line from a person or object, simulate the direction of the reflected light, and they should be centered on one spot. If not, then it might have tampered with the picture.

Fake representations of today’s society have an influence on everything from politics to medicine.

“There may be false images where there is a campaign.” Farid said, “It is normal to change the photographs in order to make the politicians appear better. The campaign team will introduce to the images several people with various skin colors, so that politicians may not appear like racists, and they may use hybrid photographs to mock rivals.”

A image like this was released during the 2004 presidential election: candidate and Vietnam veteran John Kerry (John Kerry) seated next to Jane Fonda (Jane Fonda), engaging in an anti-war protest in 1970. This illustration has been published and is also widely distributed on the Internet in several well-known newspapers. This photo, however, was later proven to be composed of two images.

This photo of politician John Kerry was faked to mislead voters

Fake photos is certainly not a new thing, the BBC has also reported this common phenomenon. In 2012, when Hurricane Sandy was raging, the BBC issued a guide to fake hurricane photos. You have probably seen a photo of the Statue of Liberty under a storm. It is indeed spectacular, but it is a pity that it is also fake. BBC columnist Rose Eveleth also talked about the way photos affect people’s memory.

When Hurricane Sandy hit New York in 2012, this modified photo began to be posted online

In fact, the modified photos have appeared since the birth of photography technology. Even the portrait of US President Lincoln is considered by many to be a composite portrait. They believe that Lincoln’s head has been moved to the body of another politician. With the popularity of digital cameras and photo editing software, this problem has become more difficult than ever.

Even the government will not let go of the opportunity to publish fake pictures-Iran has published a photo of a missile test in 2008. One of the missiles may not have been successfully launched, so the launcher in the picture that failed and caught fire was deleted. When the government uses photos of other countries as a basis for national defense decisions, its authenticity must be verified, Farid warned.

The US Department of Defense Advanced Research Projects Agency (DARPA) is trying to develop a tool to automatically detect the forgery of images and videos and assess their authenticity. Farid is a researcher on a DARPA team. He and Kevin Conner (Kevin Conner) co-founded Fourandsix, an image analysis company, in 2011. They have registered a tool called izitru, which can view the composition of the file and help determine whether the image comes directly from the camera.

Connor, who has been with Adobe for 16 years and focused on Photoshop products, said: “This technology has not yet developed to the stage where you can enter a random picture to tell you the answer. This may be difficult to achieve, but it is also the direction DARPA is working on. .”

Humans pale in comparison to identifying images. A recent study by Stanford University showed that it is difficult for students from middle school to university to identify the credibility of online information. In an experiment, the students watched a picture of what is said to be “Fukushima Nuclear Radiation Flower,” which was posted on the Internet without identifying the source. Of the 170 high school students who have seen the photos, less than 20% successfully asked the source of the photos.

This effect is not due to radiation, but a natural process called banding (fasciation).

Even if we are skeptical of the source of the image, it is still difficult for us to observe the contradiction. In a study conducted in the Brazilian state of Rio Grande do Sul, researchers showed subjects a series of photos and asked them whether the images were forged. Some of the pictures have never been processed, but more than half are synthesized: some areas are erased or contain elements copied from the same photo. The subjects had only about 47% probability of being able to recognize the fake photos.

Victor Schetinger, who participated in the research, said that his friends often come to ask him if a photo is true. He said: “According to my previous research experience, it is difficult to draw conclusions only with the naked eye. The dimensions of the photo are actually quite different. A little change can create an impactful effect. Maybe the image is very bright. There is also a strange flash, maybe there is a dust on the camera lens. You can suspect it is fake, but you can hardly assume it is fake.”

This picture of Obama was circulated in 2008, but it is fake-the clock is the clue, it originated from a TV ad in which Hillary picked up the phone at 3 o’clock

People often mistake the real for the fake and regard the fake as the real. Faried felt that people always showed fascinating self-confidence. Ignorance and confidence are the worst combination.

There are always more solutions than difficulties. Computers can help us find details that the human eye may overlook. Image identification technology uses a series of technologies and algorithms to identify fake photos by checking whether the details in the image comply with the laws of physics. Image appraisal may not be 100% correct, but experts can use multiple techniques to appraise photos at the same time.

Let’s take a look at a famous photo, which has been discussed by conspiracy theorists for decades.

Conspiracy theorists claim this Oswald photo is fake (Source: Warren Commission/Wikipedia Commons)

The photo above is of former US Marine Corps soldier Lee Harvey Oswald (Lee Harvey Oswald), who assassinated President Kennedy in 1963. Authorities stated that this photo was taken in Oswald’s backyard and was sent to his friends in April 1963. After the assassination, investigators compared the rifle in the photo with a gun found in a school warehouse in Dallas, Texas, and used it as evidence of Oswald’s guilt. Questions about the authenticity of this photo have led to a conspiracy theory that Oswald was framed as an assassin by the government or criminal gangs, especially because Oswald himself denied the authenticity of this photo and said Was shot and killed before being tried.

Conspiracy theorists point out that some of the features in the photos are “evidence” of tampering-shadows, especially those on Oswald’s face, seem to come from different light sources. Oswald’s chin looks wider than in the prison photo. Considering the weight of the gun, his stance looks strange. Others dispute the length of the gun in the photo.

Farid and colleagues studied this photo in a series of papers published in 2009, 2010, and 2015. They built a 3D model of the scene and characters based on Oswald’s prison photos, height, weight, and gun weight. They found that the shadow in the photo came from a single light source, and the shadow on Oswald’s face made his chin look wider than in the prison photo.

They also found that based on Oswald’s center of gravity and his gun style, his stance was reasonable. Considering perspective, the rifle in the photo is about 40.186 inches (101.2 cm) long, which is only less than an inch shorter than the length reported by the manufacturer. In short, the researchers found no evidence of tampering with the photos.

This is an example of the difficulty of the human visual system to make correct judgments. Farid said: “It is difficult for you to see the truth. At first glance, some aspects of the photo are really strange. This is an interesting example. What people think is not necessarily the truth-they are all physically reasonable.”

Other authentication methods have nothing to do with the content of the image, but with how the data is encoded. For example, when a photo is exported from a mobile phone or camera, it is usually packaged into a jpeg format, which is lossy compressed. Generally speaking, a photo contains a lot of data. In order to reduce the size of the file, some information will be deleted (so it is “lossy”). There are many metadata related to the photo, such as the time of shooting, the model of the camera, the preview of the thumbnail, and even the location when the photo was taken.

Pure jpeg format files do not exist, Farid explained: “Each device has a different amount of compression. iPhones compress much more than high-end SLRs. Even point-and-shoot cameras have quality settings, they create thumbnails or store metadata There are different ways. All these things will be embedded in one file.”

Law enforcement agencies often use this method to help confirm whether a photo has been modified after being exported from the camera. When using the code to view the composition of the jpeg-the order of all the information is very clear, the order of Photoshop and iPhone, Panasonic or Nikon is very different, Farid said: “Sometimes we look at the composition of the file to determine how it goes It was processed by Photoshop because the information revealed the secret.”

Can a processed photo look real by rearranging its metadata? It is possible in theory, but it is difficult to do in practice. Farid said it’s like taking all the parts of a computer apart and then putting them back together.

Farid emphasized that authentication technology does not guarantee that fake photos will always be identified. The contest between the prankster and the legal worker is like a silent arms race.

The threshold for falsification is higher than before. If the same photo can be processed through 20 different authentication techniques, when the metadata, shadows, colors and even noise are consistent, then the photo is likely to be real of.

So, what can we do to identify those fake photos circulating on the Internet? Although we can’t appraise pictures as professionally as Farid, there are still some other ways that can help us. Reverse image search (tineye.com or Google images) is a good way to determine whether a picture has been falsified by others.

However, a good photo can even fool professional news organizations. The best thing to do is to ask yourself, is it too perfect to be true? Fariddon said: “When viewing digital pictures, we’d better maintain moderate suspicion, but don’t be too aggressive. It’s easy for people to think that a real photo is fake.”