I previously mentioned the possibility that jpeg metadata could cause problems with your cropping, revealing sections of photos that you did not want to make public. Another risk that people should be aware of relates to the particular ‘signatures’ of the digital sensors inside cameras:
If you take enough images with your digital camera, they can all be compared together and a unique signature can be determined. This means that even when you think that you are posting a photo anonymously to the internet, you are actually providing clues for the government to better tell who you are. The larger the sample size of images they have, the easier it is them to track down images coming from the same camera. Once they know all the images are coming from the same camera, all they then have to do is find that camera and take a picture to confirm it beyond a reasonable doubt.
The possible implications are considerable. This technique could be used in crime fighting, though also in tracking down human rights campaigners and other enemies of oppressive states. While the linked page lists some techniques for removing the tell-tale signs, there is no guarantee they will work against any particular agency or individual who is trying to link a bunch of photos to one camera or photographer.
The take-home lesson is that anonymity is very hard in a world where so many tools can be used to puncture it.
Do you know any simple way of processing photos to remove this signature?
I suppose I should consider going back to film. Or destroying my camera after taking incriminating pictures with it.
Tristan,
Destroying your camera won’t prevent people from being able to use one photo you definitely took to prove that you also took others.
The best defence might be making a habit of lending your camera to shady criminal characters. That way, you can at least allege that someone else took the incriminating photos with your camera.
The link above goes to a page that speculates on some possible ways to remove the signature.
50 4E 47
In ASCII, the letters “PNG”, allowing a person to identify the format easily if it is viewed in a text editor.
Digital Photos Give Away a Camera’s Make and Model
“Engineers at Polytechnic University Brooklyn have discovered that digital snaps shorn of any metadata still reveal the make and model of camera used to take them. It is possible to work backwards from the relationships of neighboring pixel values in a shot to identify the model-specific demosaicing algorithm that combines red, green, and blue pixels on the sensor into color image pixels. Forensics teams are already licking their chops.”