Post-process, you know what it's all about? Assembly, selective development, retouching brush ... It does not date from yesterday, and at any time, government agencies have studied photos with some anxiety: "Is this real or not?"
For the general public, the debate is more recent but no less virulent, with some photos retouched to erase a roll of fat of some president or to lengthen the neck of some actress. It took some echo since one year with the French deputy Valérie Boyer
who bring in a bill
about the obligation to report the alterations aimed to change the aesthetics of a person.
However, in this maelstrom of opinions, there is a difficult problem to solve: how to detect alterations? This is where eXo Makina
, founded by Roger Cozien, which offers Tungstene
, an advanced interpretation software images which is able to highlight photographic modifications.The price of specializationTungstene
is not a photo software in the classical sense. It's a big mathematical tool, which operates the sampling characteristics of a camera or a compression algorithm, calculates isolines light, detects similarities or otherwise breaks in the structure of a matrix . It does not however voluntarily use classic operations that can typically be implemented in the usual development and post-production software.
It is therefore a pure analysis tool that requires special high level training where a good knowledge of photography, computing and mathematics is needed .. Its price is also equal to its specialization and still reserved for companies and administrations. However, investment is not so huge for some specifics fields ... Two other versions exist (EVIDENCE and CARBURE) that offer a simplified service and costs adjusted accordingly.
Let's take an area in which Roger Cozien, former policeman, is particularly attached: intelligence, where validate a propaganda photograph of a hostile state traditionally passed by a reconnaissance flight in F16 fighter or by the redirection of a military satellite. In some cases, be able to say "this missile was added in Photoshop
" without mobilizing the equipment save both time and resources.
Tungstene is used to analyze the way and the propagation of light on an image in order to check the consistency of informations.
Press agencies may also be interested. For them, to publish a fake photo is a serious problem, both in terms of information and of brand image. The ability to ensure, on a "hot" photo transmitted by a reporter, the reality of the document is an ethical and financial question. Agence France-Presse
(AFP) has acquired the software in order to avoid problems of edited photos seen in the press in recent years. Tungstene
is thus able, through different filters, to detect smoke added in a Jerusalem photo, an additional crowd brought in a demonstration, or otherwise ensure that the missile that is seen falling three meters above ground was actually there when the photographer started his camera.Macro-qualification
The first point checked by Tungstene is the proximity between the examined file and the original image. Firstly, by checking the correspondence between the image itself and the EXIF data: for example, if the EXIF say that the image is "as it" and the quantization tables used for the JPEG compression are those of Photoshop, then there is a problem.
Secondly, by detecting the re-sampling level of a picture. This allows not only to detect the number of re-recording of the file, but also to analyze the frequency distribution of the image and thus seek the signature of the camera used to make the shot.
Sequence analysis of the re-sampling of an image with Tungsten.
The filters are based on the algebraic structure of the image itself. The "simplest", outwardly, is intend to detect exogenous collages (from a third image) but also the endogenous cloning / duplication (of the image on itself). For that, it will examine the image area by area to find those that are not fitting or that are cloned from another piece of the picture.
Tungstene is also capable of rising to the basic structure of the file. Let us recall that most cameras only capture one color by photo-site, the other two being reconstructed during the de-mastering. Find the original structure allow to detect some collages, but also sign the use of some filters that alter this structure - and more particularly "fluidity" of Photoshop.
This is perhaps the most impressive Tungstene filter. "Isoclines" is an analysis tool of light propagation.
In the first approach, we can see it as a tool of level curves, as in cartography. Analysis of perturbations in these curves permit to detect abnormalities - to use the map analogy, an open pit mine will show the contours inconsistent with respect to the geology of the place.
However, the effects are impressive. This filter can detect most alterations, but also a simple selective development (allocation of different parameters from place to place) and cases of "over-development" (use of curves highly modified to reinforce the appearance of an image).
Another filter from the same family, called tomography, can detect components of light through a fog. Then, the internal structure of a cyclone can be reconstituted on a satellite image, whereas to the naked eye we see only a blurry area in shades of gray.
Other filters can detect the light source, sometimes difficult to find, especially when there are reflections in the image, and can also detect that the image is not an original, but the photo of a photo for example.
Interpretation to do
Tungstene is thus a powerful tool for detecting changes or developments of the image. However, Roger Cozien particular emphasis on one point: Tungstene is only a tool. It can say that a picture has been changed, re-registered, resized, or that its meta-data has been changed, but it can not tell in which way: it does not reconstruct the original image.
To imagine what damage was done and why it was made, it is the job of the software user. During the demonstrations we attended, the affirmative "here, we see that an item has been added" were followed by more ambiguous "one can imagine that the photographer wanted to do this or that the original image was like that ".
Once the technology has played a role in providing the technical assessment, eXo Makina, in collaboration with a CNRS laboratory, has developed a semiotic analysis method of the image. It's about to draw the first formal exploration and operational uses of the images that includes those where tampered with images are published. For Roger Cozien, computing, technology and semiotics are inseparable.
is constantly evolving. Nevertheless, eXo Makina has already planned to expand its capabilities. The analysis of the first videos should be referred, as this media tends to spread in the press and to be considered more reliable than the simple picture, the recent French Bettencourt case
shows that an analysis of the sound can also be useful for investigations .
It is also possible that Tungstene
leads to a simplified mode, named CARBURE, for a wider audience, and become able to scan images in an automatic way. If its creators are circumspect about the actual appropriateness of such developments - the risk to see some analysis errors or to miss an important element would obviously be increased -, the ability to process huge amount of images would be, without any doubt, a significant example in the field of intelligence, and all changes detected by an automatic scan would be good to take.
Exemples of modifications that have been made on a portrait. The green/yellow areas are identified as non-compliant with the general structure of the image: the nose, mouth and part of the hair.
Finally, it should be noted that the solely detection of the alteration is not necessarily sufficient. In the case, highly publicized with the law proposed by Valérie Boyer, of the impact of alterations on the epidemic of anorexia, it is not certain that this would be enough: an honest picture playing on lighting, makeup and selection of models with unusual morphology may have the same impact as a retouched photo.
Source: paper published in the French magazine "Focus Numérique" the 03/11/2010.