This story is a supplement to the feature "Digital Forensics: How Experts Uncover Doctored Images" which was printed in the June 2008 issue of Scientific American.

Lighting
Composite images made of pieces from different photographs can display subtle differences in the lighting conditions under which each person or object was originally photographed. Such discrepancies will often go unnoticed by the naked eye.

For an image such as the one at the right, my group can estimate the direction of the light source for each person or object (arrows). Our method relies on the simple fact that the amount of light striking a surface depends on the relative orientation of the surface to the light source. A sphere, for example, is lit the most on the side facing the light and the least on the opposite side, with gradations of shading across its surface according to the angle between the surface and the direction to the light at each point.

To infer the light-source direction, you must know the local orientation of the surface. At most places on an object in an image, it is difficult to determine the orientation. The one exception is along a surface contour, where the orientation is perpendicular to the contour (red arrows right). By measuring the brightness and orientation along several points on a contour, our algorithm estimates the light-source direction.

For the image above, the light-source direction for the police does not match that for the ducks (arrows). We would have to analyze other items to be sure it was the ducks that were added.

15 Comments

1. 1. redfoxone 05:02 PM 6/2/08

   Photoshop pictures are cool. As technology makes it easier to doctor photos, detecting them gets harder. In the latest version of Photoshop you can actually change the lighting angle.
   
   JT
   http://www.Privacy-Center.net

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2. 2. XWizBT 11:07 PM 6/2/08

   This was a fascinating read. Keep it up - tell us more!

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3. 3. Hugh Jones 11:44 PM 6/2/08

   I saw the bicyclists in your June issue. I admit the photo had me fooled, the only tipoff was the young lady's overly developed legs and the too relaxed look on her face. I suppose someone has already thought of the rather clandestine act of putting someone were they weren't, then leaving the burden of proof to them to prove they weren't. Great article!

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4. 4. Dr Abner Mality 11:51 PM 6/2/08

   You failed to point out the simplest and most obvious indicator: halination, the appearance of a halo around an object in a digital image. Halination frequently occurs when digital images are manipulated by identifying and/or sharpening edges, required for some cut and paste alterations. A good, if unresolved example, was the widely published photo of OJ in Bruno Magli loafers. The picture was taken with a film camera, not digital, yet a distinct halo was seen around OJ and his shoes.

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5. 5. lauraannq 07:52 PM 6/3/08

   Having edited so many photos in my time, spoting edited photos has become easier but as one redfoxone mentioned new versions of photoshop and corel paintshop pro photo come out it becomes harder and harder to find the fakes. Your programs sound great and I would love to see them in action on more photos... especially during the election.
   
   lauraannq
   http://biscuitq.blogspot.com

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6. 6. teephil 05:06 PM 6/4/08

   Your article "Digital Image Forensics" SA, June 2008, could have picked a better example than the clumsily altered photo of the cyclists. It doesn't need digital techniques to spot a number of errors, including the lighting inconsistencies discussed in the article. Her neck appears to be growing too far down and on the right hand side of the chest, and it's incorrectly aligned with the rotation of the shoulders. Her facial features seem too fine for the broad male shoulders and chest she has been grafted onto. Her hair seems remarkably composed for someone supposedly flying along a road, and everyone else seems to need to sport a brand of goggles of some kind, why should she be any different? And in the background the fire hydrant appears to have been photographed from ground level, inconsistent with the shoulder height viewpoint of the main view.

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7. 7. VFX CSN0309 11:32 AM 7/11/08

   I think it's hard to identify such those faked picture even though to use some kind of so-call high-tech, because the computer graphics technology, people can use software to make fake. Such as, 3Dmax, maya or XSI etc. Those software can output a large unmber of picture as a sequence and finally put it together as a film. For example, "The day after tomorrow","Transformers" and so on. Those film are all relied on the computer graphics technology to make 'fake' and also to 'deceive' the audience. In addition, the HDRI(High dynamic range imaging ), This technology can be provided for faker to get some accurate light information from where he/she want to make fake whether or not any foul light condition.
   For instance http://forums.cgsociety.org/showthread.php?f=132&t=636028

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8. 8. Trisha143 08:47 PM 7/11/08

   This was a very ineresting article. I'll be looking more closely at photos. I do now, the news hypes things up way too much as it is.
   

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9. 9. Ben 02:44 AM 9/2/08

   This was an interesting article. While many of the techniques were familiar to me, the section on digital fingerprints was new. There is a small editorial mistake, though. (38+42+40)/4 does not equal 38. The correct equation is (38+42+40+32)/4 = 38.

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10. 10. isoal 08:03 PM 7/26/09

    Omgg tha is defo real , how can you not belive that ?

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11. 11. isoal 08:07 PM 7/26/09

    mell and teagn are cool (:

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12. 12. Ultcritic 08:32 PM 1/22/10

    Fascinating article. Eye opening info. Have you ever studied the (in)famous photo of Lee Harvey Oswald holding a rifle and a pistol using these techniques? What was the result? There are conflicting shadows in that photo.

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13. 13. corticalchaos 04:52 PM 4/7/10

    ive seen many shoops in my time and i know from the pixels that this image is a shoop

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14. 14. jession521 10:45 PM 9/10/10

    I am a student and my major is image forensics.Could you send me some source code about this!?

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15. 15. jession521 10:46 PM 9/10/10

    I need some source code about image forensics and thanks for your help!!!

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