Identifying Manipulated Images

Jamie found a cool story at MIT Tech Review. (As an aside, it sits behind an interstitial ad AND on 2 pages: normally I reject websites that do that, but it's a slow news day, so I'm letting it through.) Essentially, software is used to analyze light patterns in still photographs. Once you can figure out where the light sources are, it becomes a lot easier to determine if an image has been photoshopped.

Comments

Steganography

[unbug]

Does it also apply to steganography? Would sort of suck if it did.

Expert User Required

[Anonymous Coward]

TFA says an "expert user" is required. This expert user inputs coefficients that drive the equations that analyze the picture.

So basically, if you want an image to be doctored, you use one set of values. If you want an image to be genuine, you use another set of values. Maybe somebody else's requirements differ from mine, but this is not the kind of flexibility I want in a tool that is supposed to tell me if an image has been altered or not.

For an example of a better tool, see this article from Slashdot in August 2007.

Goes both ways

[Nerdposeur]

...and then the photoshoppers will write evolutionary algorithms to modify their photographs until they pass evaluation by this tool.

Adds a step for the photoshoppers

[crowemojo]

One would think that it would be simple enough, after finishing whatever touch-ups that you want to perform, that you use this technique to calculate where the light sources should be, and then correct the minute details that would give it away as an altered image. Sounds like the kind of thing that would be a simple photoshop plugin actually, once you are all done you just run the "make undetectable from light source detection analysis" tool and call it a day.

Re:Adds a step for the photoshoppers

[Anonymous Coward]

This algorithm at least requires human intervention, to find contours (RTFA). Additionally, it's easier to find inconsistencies than to automatically resolve them in a way which doesn't cause potentially something else to look weird.

It's just another tool which requires (some) human ingenuity to use effectively and thus requires (just a little more) human ingenuity to use offensively. After all, you only need to miss one detail to be found out... and hiring a photodoctoring expert is something you don't want to do if you (e.g. news media) are trying to sneak this past the public. I'd say that it's not as symmetric as you suggest.

You can come up with a lot of confounding examples for this method anyway - imagine if one of the subjects in your photo has a flashlight, or is illuminated by a spotlight. "Make undetectable from light source analysis" (or "Detect Forgery by Light Source Analysis" for that matter) is something I'll expect to see in CSI, not reality.

Re:Limited utillity

[aadvancedGIR]

Moreover, it is well known that photoshop is a standard and commonly used tool for professional studio photography anyway. I think the tool purpose is limited to check that a "genuine" photography used to prove a crime or the existence of UFO/Bigfoot is not a blatant fake.

Re:Based on the same codebase, in fact

[Neotrantor]

horse shit

changing the light source in a picture requires that you might have to desaturated some pixels and guess what their level/color might be, which is information you probably don't have available.

Re:Good

[dotancohen]

That's why I say "to gimp a photo" rather than say "to photoshop a photo". It spreads awareness, breaks the Adobe monopoly, and sounds more natural. Even Adobe discourages the use of "photoshop" as a verb.

Re:Good

[m.ducharme]

Even Adobe discourages the use of "photoshop" as a verb. You know why, right? If they let "photoshop" be corrupted in the language as a verb, they would eventually lose the trademark rights to the name. Eventually, companies would be able to get away with naming their software "MS Photoshopping Program" or "Gimp Photoshop Utility" or whatever, and Adobe wouldn't be able to do anything about it.

Are you sure now, that you want to discourage people from using "photoshop" as a verb?

"photoshopped"?

[Lxy]

When did "photoshop" become a verb?

This post has been gimped by the gimper

Re:Detector == Quality Control

[xquark]

If they can automate the detection then they can as easily automate the circumvention.