The fingerprint inside your photos

When considering these privacy issues, we might draw parallels with another technology. Many colour printers add secret tracking dots to documents: virtually invisible yellow dots that reveal a printer's serial number, as well as the date and time a document was printed. In 2017, these dots may have been used by the FBI in the identification of Reality Winner as the source of a leaked National Security Agency document, which detailed alleged Russian interference in the 2016 US presidential election.

Regardless of your opinion on whistleblowing, these surveillance techniques could affect us all. The European Commission has voiced concerns, suggesting that such mechanisms could erode an individual's "right to privacy and private life". If we view photo fingerprints as being equivalent to a printer's serial number, then this prompts us to ask whether photo response non-uniformity also violates an individual's right to protection of their personal data.

Despite our chronic predisposition to self-disclose over the internet, we vehemently reserve the right to privacy. In principle, people should be able to decide the degree to which information about themselves is communicated externally. But in light of what we now know about forensic photo tracking, such self-determination may only be an illusion of control.

Standard metadata is difficult enough to avoid – you have to scrub it afterwards, and the only piece of information you can stop from being created in the first instance is photo geolocation. Photo response non-uniformity, however, is far more difficult to extricate. Technically, it should be possible to suppress, for example, by reducing the image resolution, says Farid. But, by how much? This of course depends on many factors such as the type of device used for image capture, as well as the fingerprint matching algorithm employed. There is no one-size-fits-all solution to fingerprint removal.

So, how concerned should we be about photo response non-uniformity from an ethical standpoint? When I asked Fridrich about the implications of its various applications, she candidly remarked, "a carpenter can do wonders with a hammer, but a hammer can also kill". While no one is saying that the hidden data inside your photos could be deadly, her point is that this is a technique that could cause harm in the wrong hands.

You don't need to be Donald Trump or John McAfee to be affected by the rise of photo metadata and fingerprints. So the next time you take a snap with your smartphone, you might pause to reflect on how much more is being captured than what you see through the lens.

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Jerone Andrews wrote this article while working as a researcher at University College London, as part of a media fellowship organised by the British Science Association.

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