Is it possible to take two identical photos?

Question

Let's say for example: there is a really nice photograph by a pro photographer of a famous landmark. Somebody wants to put a photo of this landmark on their website. They decide to steal the photograph of the pro photographer and put it on their website. If caught, the punishment will be 1 million dollars.

Now lets assume that sometime in the future, the pro photographer complains, saying this website stole his photo. It goes to court, and now you are the jury. You need to decide was it stolen, or did the person take it himself. You need to prove it 100%.

The defense: the photograph was taken of a public building, using certain exposure settings, ISO settings, focal length, etc etc, and the same type of camera. You took the photograph and it just coincidentally turns out to be the same. And so the two photos look identical.

Is this possible in real life? Is it possible that two photos could be identical (not by chance, but by trying)? Could you exactly recreate somebody's photograph? If you scan the photograph to analyse the lighting, every little part of light, would it be impossible to recreate it exactly the same way?

Can the jury prove that the photograph is actually just a stolen copy of the pro photographers? Or can the defense win this case, and by not being able to be proven 100% guilty, escape a million dollar fine, by convincing the jury that it was a coincidence?

A scientist is also in the courtroom. He makes a demonstration. There is a stool with a mug on it. He takes a photograph of it. Then he takes another photograph. Is it possible that both photographs will be identical, to the point that a computer analysing them will not be able to find any difference? Will his test pass or fail?

Answer 1

Let's take this step by setp:



a lot of people here were stating that the EXIF data could be used to verify the picture. Sorry, but no. EXIF data are not cryptographcally secured, so they can be manipulated quite easily. For people who need unforgeable digital pictures (usually epert witnesses), there are digital cameras out there that will add a cryptographic key to the image data, which have so far been impossible to falsify. No guarantees for the future, though - with the advent of quantum computing, this kind of encryption/authentication would also need to incorporate some form of quantum encryption.



Analogue (i.e. film) photography is usually secure from this angle. It could be manipulated, sure - but only as long as you won't have the negatives forensically examined.



Now, looking only at the image data. Let's assume each of the two contestants has brought their original image - either the negative, the RAW dataset or the JPEG - to the courtroom. The problem now is to determine whether the picture on the website, which most likely is a reduced resolution JPEG image, is derived from either the one or the other.



As in all scientific processes, you won't be able to get 100% confidence in either outcome.



But if the two 'originals' were taken at a different time, with a different camera, there will be differences in the originals. At the very least, the noise pattern of the sensor would be different, at the most, the image contents themselves would be different (imagine the leaves of a tree moving in the wind, or the sun shining at a different angle). The problem is now, are those differences large enough to survive the compression/size reduction process that lead to the website image? If not, the two resulting compressed pictures are indistinguishable.



As an example: imagine taking that picture of a stone on desk, in a closed room (no windows, controlled artificial light from a DC source) twice in a row. Delete the EXIF data, only keep the RAW image data. Imagine that the camera uses a very good 14 bit sensor/ADC and that the exposure is perfect, so that all of the noise is in the lowest 4 bit of ADC output. Now run that image through a 8 bit JPEG compression. The lowest 5 bits of sensor information are discarded, the 6th bit is used for rounding - all of the difference information is lost.



So, while you can easily distinguish the two originals, it will be impossible to distinguish the compressed images created from the two originals - in this special case.



Again, for the real life case, it boils down to whether the differences between the pictures are large enough to survive the compression process. Usually, they will be - at least for any picture worth fighting over.



As for the software to detect the differences: as long as you have the images as digital data, a simple diff operation (i.e. subtract one image from the other - binary) will show you the differences at once.



As to your argument that 'the computer' 'believes' that the two pictures are identical: it will only do so if manipulated. Prosecution could request either a detailed software audit, demonstrate the comparison of the two RAW data sets themselves or show a similarly manipulated experiment. But the problem for the prosecution remains: defense can easily show that two different originals can result in two identical compressed images (on the binary level), thereby winning the case under the assumption of 'inncent until proven guilty'.

Answer 2

If the exif data (metadata) was available, you could certainly prove that it is an original photo and not a stolen photo.



However, I am of the opinion that you could never go back to the same scene and absolutely duplicate a photo. There might be clues to differentiate the two images like the shadow positions, the direction of the light source, a reflection in a window, the position of clouds if there are any present, slight variation in perspective, to name the things I can think about right now.



If you did not examine the exif data, I believe that it IS possible to take an image that is a duplicate of one of your own, if you take it at virtually the same time. If you have your camera on a tripod and use a cable release, it can be done. If you use a continuous shooting mode at a higher speed (like 6-to-8 frames per second), you could probably even do it hand-held.



There is an option to turn "authentification" on in my camera. This creates a unique digital signature in the exif data that will show (using Nikon software) if the image has been modified in any way. For those who are aware of it, this is really the only acceptable way to provide digital images as evidence in court. Forensic photographers should use this option all the time. I assume that the other brands have a similar feature.

Answer 3

If the EXIF data was intact you can prove that your camera took the shot, the EXIF data records much more than just the settings, it also records the serial number of the camera and lens, the date it was made, the production line it was made on, the number of shutter activations and a whole load of other data, even date and time the image was shot, on some cameras even the GPS of where you were standing to take the shot.



All this info is available in the original file, it won't be available if it has been stripped out, but that on it's own is suspicious.



If there are any people in the frame and the date and time is known, people are creatures of habit and if you return a week later chances are the same people will pass the same point at roughly the same time, these could be questioned to prove either way.



Getting exactly the same image on different days is virtually impossible, even on the same day, a few minutes alters the angle of the Sun which can be measured from the shadows (the extended version of Photoshop has these forensic tools (and more) and is sometimes used for just this purpose), the light level is constantly altering due to clouds etc. which alters settings.



Chris

Answer 4

If the exif information is still in tact the photographs could be identified as different, but I assume it is possible to modify the exif information.



The possibility of getting two pictures identical especially taken outside on different days is almost impossible (Actually impossible). There will be minor differences in the lighting and shadows. The picture would have to be taken at the exact time of day to have the exact same shadows, if it was shot at the same time of day a week or two apart, the shadows would still be different.



Through close examination of the image would show differences if the pictures were duplicates or each other. Now depending on how the image was edited, the final process image can be made to look slightly different by changing or modifying light sources.



By overlaying the images, one could find out if they are duplicates or originals. If made the same size, (in a blown up size) and overlaid, you should see the outline of the structure not matching. If it matches, one of the images is a duplicate of the other.



The only way to be almost identical would be to use a mounting structure to hold each camera in place while taking the shot, but this does not guarantee the shots to be exact either.



So draw your own conclusions.



Best wishes.

Answer 5

Yes it is possible to have the same exact photograph taken by two different individuals using different cameras.



If you don't want your photo to be stolen, don't post it in the internet. The internet is public. A picture of a famous landmark taken in public can hardly be claimed as yours. Anyone can do it. Again, there is that public factor. It is up to the original photographer to safeguard his work. This case would not even reach the courts. It would be a waste of time and money. The judge won't hear a single word of it. Scientist? Why? Computer analysis? What?



You must have too much time on your hands to even go that deep about this. I know. I have mine.

Answer 6

Nope.



Quantum fluctuations insure no two separately-taken photographs will ever be completely identical.

And even in the age of digital imaging, all you need to do is keep your RAW file around, and you have your "100% proof."



Peace.

Answer 7

Why the hell are you tolerating anyone who openly admits to hating one of your facial features? I think you need to apprise this dude he's entirely out of tact, severe all ties with him, and embrace your nose for giving you a little bit of individuality.