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PhotoDNA is a technology developed by Microsoft and improved by Hany Farid professor at Dartmouth College that computes hash values of images, video and audio files to identify similar images.[1]

PhotoDNA is primarily used in the identification of child pornography, and works by computing a unique hash that represents the image. This hash is computed such that it is resistant to alterations in the image, including resizing and minor color alterations.[1] It works by converting the image to black and white, resizing it, breaking it into a grid, and looking at intensity gradients or edges.[2]

It is used with Microsoft's own services Bing and OneDrive,[3] as well as by Google Gmail, Twitter,[4] Facebook,[5] Adobe Systems,[6] Reddit[7] and the National Center for Missing & Exploited Children,[8] 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.[9][10][11][12] Project VIC uses the technology to create a "fingerprint" that can be used to uniquely identify an individual photo.[9][12][13] 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.[11][14] The technology also assists online service providers, by helping them detect child sexual abuse images shared on their sites, and block their continued dissemination.[13][15][16]

In December 2014, Microsoft also made PhotoDNA available to qualified organizations as a free cloud service through the Azure Marketplace.[17]

In late 2015, Farid completed improvements to the software which now make it capable of analyzing video and audio files besides still images.[citation needed] In 2016, Hany Farid proposed that the technology could be used to stem the spread of terror-related imagery, but there was little interest shown initially by social media companies.[18] 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,[19] which was done e.g. to automatically remove al-Qaeda videos.[20]


  1. ^ a b "New Technology Fights Child Porn by Tracking Its "PhotoDNA"". Microsoft Corporation. Retrieved September 9, 2016.
  2. ^ "Photo DNA: Step by step". Microsoft. Archived from the original on September 21, 2013. Retrieved February 11, 2014.
  3. ^ "Unfortunate Truths about Child Pornography and the Internet [Feature]".
  4. ^ Arthur, Charles (July 22, 2013). "Twitter to introduce PhotoDNA system to block child abuse images". The Guardian. Retrieved July 22, 2013.
  5. ^ Smith, Catharine (May 2, 2011). "Facebook Adopts Microsoft PhotoDNA To Remove Child Pornography". Huffington Post. Retrieved July 22, 2013.
  6. ^ "Adobe & PhotoDNA". Archived from the original on February 22, 2018.
  7. ^ "Reddit use PhotoDNA to prevent child pornography". March 19, 2020.
  8. ^ Salcito, Anthony (December 17, 2009). "Microsoft donates PhotoDNA technology to make the Internet safer for kids". Retrieved July 22, 2013.
  9. ^ a b "New Video Fingerprinting Technology Created to Remove Child Pornography Online". MarketWatch. April 30, 2014.
  10. ^ William Jackson (August 27, 2014). "Improved image analysis tools speed exploited children cases". GCN.
  11. ^ a b "New Fingerprinting Technology to Remove Child Pornography Online"[permanent dead link], Friend Media Technology Systems
  12. ^ a b Liat Clark (April 30, 2014). "Child abuse-tracking tech donated to the world". Wired UK.
  13. ^ 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
  14. ^ Mark Ward (March 23, 2014). "Cloud-based archive tool to help catch child abusers". BBC News.
  15. ^ 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 1119996201.
  16. ^ Marcia Lattanzi-Licht; Kenneth Doka (2004). Living with Grief: Coping with Public Tragedy. Routledge. p. 317. ISBN 1135941513.
  17. ^ "PhotoDNA Cloud Service". Microsoft Corporation. Retrieved February 19, 2015.
  18. ^ Waddell, Kaveh (June 22, 2016). "A Tool to Delete Beheading Videos Before They Even Appear Online". The Atlantic. Retrieved September 10, 2016.
  19. ^ "Partnering to Help Curb Spread of Online Terrorist Content | Facebook Newsroom". Retrieved December 6, 2016.
  20. ^ Richard Allan of Facebook (June 18, 2018). "Hearing at 11:14". in "The EU's horizontal regulatory framework for illegal content removal in the DSM".

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