New Technique Analyzes Shadows to Spot Photo Fakes

INSIDE SCIENCE NEWS SERVICE ^ | Aug 14 2013 | Ker Than

[neverdem]

Algorithm spots forgeries by spotting shadows that don't match light sources.

(ISNS) -- A new algorithm can spot fake photos by looking for inconsistent shadows that are not always obvious to the naked eye.

The technique, which will be published in the journal ACM Transactions on Graphics in September, is the latest tool in the increasingly sophisticated arms race between digital forensics experts and those who manipulate photos or create fake tableaus for deceptive purposes.

National security agencies, the media, scientific journals and others use digital forensic techniques to differentiate between authentic images and computerized forgeries.

James O'Brien, a computer scientist at the University of California, Berkeley, along with Hany Farid and Eric Kee of Dartmouth University, developed an algorithm that interprets a variety of shadows in an image to determine if they are physically consistent with a single light source.

In the real world, O'Brien explained, if you drew a line from a shadow to the object that cast the shadow and kept extending the line, it would eventually hit the light source. Sometimes, however, it isn't possible to pair each portion of a shadow to its exact match on an object.

"So instead we draw a wedge from the shadow where the wedge includes the whole object. We know that the line would have to be in that wedge somewhere. We then keep drawing wedges, extending them beyond the edges of the image," said O'Brien.

If the photo is authentic, then all of the wedges will have a common intersection region where the light source is. If they don't intersect, "the image is a phony," O'Brien said.

A growing toolbox

The new technique does have limits, though. For instance, it was designed for use with images in which there is a single dominant light source, not situations with lots of little lights or a wide, diffuse light.

One could also imagine a clever forger anticipating the use of the shadow detection software and making sure they created shadows that would pass the test. The researchers call this just one technique in a toolbox of methods that are being developed to catch forgers.

O'Brien says one of the motivations for developing their algorithm is to reduce the need to rely on subjective evaluation by human experts to spot forgeries, which can easily mistake forged photos for authentic photos and authentic photos for forged ones.

Take for example the iconic 1969 photo of NASA astronaut Buzz Aldrin posing on the surface of the moon.

"The shadows go in all kinds of different directions and the lighting's very strange...but if you do the analysis [with our software], it all checks out," O'Brien said.

Our trouble with shadows

It's unclear why humans are so bad at detecting inconsistent shadows, especially since our visual systems are so attuned to other cues, such as color, size and shape, said UC-Berkeley vision researcher Marty Banks.

One idea, Banks said, is that shadows are a relatively unimportant visual cue when it comes to helping organisms survive.

"It's important to get the color right because that might be a sign that the fruit or meat you're going to eat is spoiled, and it's important to get size and position right so you can interact with things," said Banks, who did not participate in the research. "And then there are things where it just doesn't really matter. One of them is shadows, we believe."

After all, before the advent of photography, one was unlikely to ever encounter a scene where the shadows are pointing in the wrong direction.

Analyzing shadows could also just be a more mentally taxing task, said Shree Nayar, a computer vision researcher at New York's Columbia University, who was also not involved in the research.

"This is a more complex second order effect," Nayar said, "and it's something we have a much harder time perceiving."

Man-machine collaboration

For now at least, the team's method still requires some human assistance, by matching shadows to the objects that cast them.

"This is something that in many images is unambiguous and people are pretty good at it," O'Brien explained.

Once that is done, the software takes over and figures out if the shadows could have been created by a common light source.

In this way, the scientists say, their method lets humans do what computers are poor at — interpreting the high-level content in images — and lets computers do what humans are poor at — testing for inconsistencies.

"I think for the foreseeable future, the best approaches are going to be this hybrid of humans and machines working together," O'Brien said.

Columbia's Nayar said he could envision a day when computers won't need human assistance to perform such tasks, because of increasingly sophisticated models and machine learning algorithms.

Because their software requires relatively simple human assistance, O'Brien and his team say it could one day be useful not only to experts, but the general public as well.

"So you could imagine a plug-in for Photoshop or an interactive app in your web browser where you can do that, and it would flag any inconsistencies," O'Brien said.

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Ker Than is a freelance writer based in Southern California.

[gopheraj]

Why would Obama be holding a basketball? The kid in front has one. IMO, he would not have been holding a ball in the team pic.

[Albertafriend]

One thing that has always betrayed this photo as a fake is that tiny seemingly insignificant triangle of light blue between 0 and Grandpa’s shoulders. There is absolutely no reason for anything to be blue there!

[sun7]

Now that you mentioned it, yes, the shadow across his shoulders is a big one.

So in the final analysis, shadows are the biggest giveaway after all. The other shadow I mentioned in post #44 was so complete I didn’t even notice there was a ball underneath his hands. Now the ball must be levitating in the air.

By the way, I must scratch item #2 from my original list. I didn’t see the youth’s forearm at first and thought it was missing.

Unlike obama’s alleged childhood photos which are in color and look contemporary, both team photos (post #22 and #54) are b/w, grainy, and resemble old WWII era photos. Apparently, they decided to use very old photos to minimize the chance someone will emerge with the real photos. One can only count on family members to keep the secrets after all.

[Larry - Moe and Curly]

“I can’t find anything wrong with that picture...”

Look at the shadows behind their feet. Moochelle’s goes straight back, Barry’s go to the left at an angle.

[Fred Nerks]

That patch of wall that shouldn't be there was placed where it is to fool the eye into accepting that Stanley Armour's arm wasn't at his side; it's the only way the eye can be fooled into accepting that fake hand on zero's shoulder.

For every fake there's a need.

The need was to show there was still a relationship between the Dunhams and zero at the time he was in New York.

There wasn't. There is no more evidence of any kind of them ever being together after that obvious fake in Central Park. The last genuine photograph of the Dunhams with zero might have been the one at his graduation in Hawaii in 1979.

They took a photo of him sitting with his back to the lake, and posed him so that he would fit between the Dunhams:

And that's why the sun is shining on his hand:

[Ditter]

Look again hers do too.

[Fred Nerks]

There are many images of them on that visit, all of them equally hideous. And now you'll say look, he's got four legs and two right hands!

[Fred Nerks]

Oh look, they found an Indonesian garden-gnome!

[Ditter]

LOL! Yes he does, you are right. She had an extra right hand coming off Airforce 1 and he decided he wanted an extra hand. Why are they cutting people out of these photographs? And where did she get that awful green pantsuit? I want to know so I will never shop there.

[Ditter]

LOL! Well you found the extra legs and feet but we still don’t know about the green pantsuit.

[uncitizen]

Was he supposedly married already at the time of this picture? He is wearing his “wedding” ring after all....

[King Moonracer]

Did Obama’s head shrink? As a kid, his head is ginormous, but as an adult it’s average to less than average. Heads don’t shrink.

[thecodont]

Creepy!

[thecodont]

The shadow behind her right leg is cut off — it stops abruptly, so you can see a vertical dividing line between her and BO. The shadow behind her left leg goes off at an angle behind her and looks normal.

[thecodont]

The shadow behind her right leg is cut off — it stops abruptly, so you can see a vertical dividing line between her and BO. The shadow behind her left leg goes off at an angle behind her and looks normal.

[Fred Nerks]

It’s not a wedding ring, it’s an African-elephant-hair ring, made in gold. It’s a piece of traditional african jewelry.

[Fred Nerks]

There are a number of images of that visit to Indonesia on Google Images, why don’t you download them all and look at the shadows? It will help to take your mind off the ugly pants-suit and current world events.

[Fred Nerks]

AFRICAN ELEPHANT HAIR RING JEWELRY ON GOOGLE. LINK

[Heart-Rest]

That picture brings to mind this old TV commercial:

  It Takes Two Hands To Handle A Whopper-Teller

[uncitizen]

thanks for straightening that out for me.