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PhotoDNA Process

PhotoDNA is an image-identification technology used for detecting child pornography and other illegal content reported to the National Center for Missing & Exploited Children (NCMEC) as required by law.[1] It was developed by Microsoft Research and Hany Farid, professor at Dartmouth College, beginning in 2009. From a database of known illegal images and video files, it creates unique hashes to represent each image, which can then be used to identify other instances of those images.[2]

PhotoDNA is primarily used in the identification of child pornography (also known as child sexual abuse material or CSAM), and works by computing a unique hash that represents a given image. This hash is computed such that it is resistant to alterations in the image, including resizing and minor color alterations.[2] It works by converting the image to black and white, resizing it, breaking it into a grid, and then looking at each cell's intensity gradients or edges.[3]

It is used on Microsoft's own services including Bing and OneDrive,[4] as well as by Google's Gmail, Twitter,[5] Facebook,[6] Adobe Systems,[7] Reddit,[8] Discord[9] and the NCMEC,[10] to whom Microsoft donated the technology.

Microsoft donated the PhotoDNA technology to Project VIC, managed and supported by the International Centre for Missing & Exploited Children (ICMEC). Project VIC is an image and video hash-sharing initiative that streamlines investigative workflows and narrows the focus of child pornography law enforcement investigations by filtering the material investigators find on offenders’ computers.[11][12][13][14] Project VIC uses the technology to create a "fingerprint" that can be used to uniquely identify an individual photo.[11][14][15] Using robust hash sets, the technology allows law enforcement to determine which images retrieved have already been identified, and are part of the Project's database of millions of digital hashes of child pornography, enabling detectives to focus on those that are new children waiting to be located and recovered.[13][16] The technology also assists online service providers by helping them detect child sexual abuse images shared on their sites, and halt their continued dissemination.[15][17][18]


In December 2014, Microsoft also made PhotoDNA available to qualified organizations as a free cloud service through the Azure Marketplace.[19]

In late 2015, Microsoft completed improvements to the software which now make it capable of analyzing video files as well as still images.[20]

In 2016, Hany Farid proposed that the technology could be used to stem the spread of terror-related imagery, but little interest was initially shown by social media companies.[21] In December 2016, Facebook, Twitter, Google and Microsoft announced plans to use PhotoDNA to tackle extremist content such as terrorist recruitment videos or violent terrorist imagery,[22] which was done e.g. to automatically remove al-Qaeda videos.[23]

Technical details[edit]

Photo DNA Video Solution

The PhotoDNA helps to reduce online recirculation by creating a “hash” or digital signature of an image: converting it into a black-and-white format, dividing it into squares, and quantifying the shading of the squares. It does not employ facial recognition technology, nor can it identify a person or object in the image. It compares an image’s hash against a database of images that watchdog organizations and companies have already identified as illegal. The UK Internet Watch Foundation, which has been compiling a reference database of PhotoDNA signatures, now has 300,000 hashes of known child sexual exploitation materials.

PhotoDNA for Video breaks down a video into keyframes and creates hashes for those screenshots. In the same way that PhotoDNA can match an image that has been altered to avoid detection, PhotoDNA for Video can find child sexual exploitation content that has been edited or spliced into a video that might otherwise appear harmless. PhotoDNA for Video can find embed illegal videos in other videos based on one or more hashes of keyframes. [24]


Content providers use PhotoDNA to remove millions of illegal photographs from the internet. It has helped law enforcement to convict child sexual predators and rescue potential victims before they are physically harmed. [25]


  1. ^ "Microsoft tip led police to arrest man over child abuse images". The Guardian. August 7, 2014.
  2. ^ a b "New Technology Fights Child Porn by Tracking Its "PhotoDNA"". Microsoft Corporation. December 15, 2009. Retrieved September 9, 2016.
  3. ^ "Photo DNA: Step by step". Microsoft. Archived from the original on September 21, 2013. Retrieved February 11, 2014.
  4. ^ "Unfortunate Truths about Child Pornography and the Internet [Feature]". December 7, 2012.
  5. ^ Arthur, Charles (July 22, 2013). "Twitter to introduce PhotoDNA system to block child abuse images". The Guardian. Retrieved July 22, 2013.
  6. ^ Smith, Catharine (May 2, 2011). "Facebook Adopts Microsoft PhotoDNA To Remove Child Pornography". Huffington Post. Retrieved July 22, 2013.
  7. ^ "Adobe & PhotoDNA". Retrieved August 27, 2021.
  8. ^ "Reddit use PhotoDNA to prevent child pornography". March 19, 2020.
  9. ^ "Discord Transparency Report: July — Dec 2020". Discord Blog. April 2, 2021. Retrieved May 8, 2022.
  10. ^ Salcito, Anthony (December 17, 2009). "Microsoft donates PhotoDNA technology to make the Internet safer for kids". Retrieved July 22, 2013.
  11. ^ a b "New Video Fingerprinting Technology Created to Remove Child Pornography Online". MarketWatch. April 30, 2014.
  12. ^ William Jackson (August 27, 2014). "Improved image analysis tools speed exploited children cases". GCN.
  13. ^ a b "New Fingerprinting Technology to Remove Child Pornography Online"[permanent dead link], Friend Media Technology Systems
  14. ^ a b Liat Clark (April 30, 2014). "Child abuse-tracking tech donated to the world". Wired UK.
  15. ^ a b "Microsoft's response to the consultation on the European Commission Communication on the Rights of the Child (2011–2014)" (PDF). Archived from the original (PDF) on October 24, 2017., European Commission
  16. ^ Mark Ward (March 23, 2014). "Cloud-based archive tool to help catch child abusers". BBC News.
  17. ^ Reinhard Eher; Leam A. Craig; Michael H. Miner; Friedemann Pfäfflin (2011). International Perspectives on the Assessment and Treatment of Sexual Offenders: Theory, Practice and Research. John Wiley & Sons. p. 514. ISBN 978-1119996200.
  18. ^ Marcia Lattanzi-Licht; Kenneth Doka (2004). Living with Grief: Coping with Public Tragedy. Routledge. p. 317. ISBN 1135941513.
  19. ^ "PhotoDNA Cloud Service". Microsoft Corporation. Retrieved February 19, 2015.
  20. ^ "How PhotoDNA for Video is being used to fight online child exploitation". September 12, 2018.
  21. ^ Waddell, Kaveh (June 22, 2016). "A Tool to Delete Beheading Videos Before They Even Appear Online". The Atlantic. Retrieved September 10, 2016.
  22. ^ "Partnering to Help Curb Spread of Online Terrorist Content | Facebook Newsroom". Retrieved December 6, 2016.
  23. ^ Richard Allan of Facebook (June 18, 2018). "Hearing at 11:14". {{cite news}}: |author= has generic name (help) in "The EU's horizontal regulatory framework for illegal content removal in the DSM".
  24. ^ "How PhotoDNA for Video is being used to fight online child exploitation". September 12, 2018.
  25. ^ "How PhotoDNA for Video is being used to fight online child exploitation". September 12, 2018.

External links[edit]