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PhotoDNA is a proprietary image-identification and content filtering technology[1] widely used by online service providers.[2][3]


PhotoDNA was developed by Microsoft Research and Hany Farid, professor at Dartmouth College, beginning in 2009. From a database of known images and video files, it creates unique hashes to represent each image, which can then be used to identify other instances of those images.[4]

The hashing method initially relied on converting images into a black-and-white format, dividing them into squares, and quantifying the shading of the squares,[5] did not employ facial recognition technology, nor could it identify a person or object in the image.[citation needed] The method sought to be resistant to alterations in the image, including resizing and minor color alterations.[4] Since 2015,[6] similar methods are used for individual video frames in video files.[7]

Microsoft donated[failed verification] the PhotoDNA technology to Project VIC, managed and supported by the International Centre for Missing & Exploited Children (ICMEC) and used as part of digital forensics operations[8][9] by storing "fingerprints" that can be used to uniquely identify an individual photo.[9][10] The database includes hashes for millions of items.[11]

In December 2014, Microsoft made PhotoDNA available to qualified organizations in a software as a service model for free through the Azure Marketplace.[12]

In the 2010s and 2020s, PhotoDNA was put forward in connection with policy proposals relating to content moderation and internet censorship,[13] including US Senate hearings (2019 on "digital responsibility",[2] 2022 on the EARN IT Act[14]) and various proposals by the European Commission dubbed "upload filters" by civil society[15][16] such as so-called voluntary codes (in 2016[17] on hate speech[18] after 2015 events, 2018[19] and 2022[20] on disinformation), copyright legislation (chiefly the 2019 copyright directive debated between 2014[21] and 2021[22]), terrorism-related regulations (TERREG)[23] and internet wiretapping regulations (2021 "chat control").[24]

In 2016, Hany Farid proposed to extend usage of the technology to terrorism-related content.[25] In December 2016, Facebook, Twitter, Google and Microsoft announced plans to use PhotoDNA to remove extremist content such as terrorist recruitment videos or violent terrorist imagery.[26] In 2018 Facebook stated that PhotoDNA was used to automatically remove al-Qaeda videos.[13]

By 2019, big tech companies including Microsoft, Facebook and Google publicly announced that since 2017 they were running the GIFCT as a shared database of content to be automatically censored.[2] As of 2021, Apple was thought to be using NeuralHash for similar purposes.[27]

In 2022, The New York Times covered the story of two dads whose Google accounts were closed after photos they took of their child for medical purposes were automatically uploaded to Google's servers.[28] The article compares PhotoDNA, which requires a database of known hashes, with Google's AI-based technology, which can recognize previously unseen exploitative images. [29][30]


Microsoft originally used PhotoDNA on its own services including Bing and OneDrive.[31] As of 2022, PhotoDNA was widely used by online service providers for their content moderation efforts[10][32][33] including Google's Gmail, Twitter,[34] Facebook,[35] Adobe Systems,[36] Reddit,[37] Discord.[38]

The UK Internet Watch Foundation, which has been compiling a reference database of PhotoDNA signatures, reportedly had over 300,000 hashes of known child sexual exploitation materials.[citation needed] Another source of the database was the National Center for Missing & Exploited Children (NCMEC).[39][40]

PhotoDNA is widely used to remove content,[2] disable accounts and report people.[7] In 2021, Google alone was reported to have filed 600,000 reports of CSAM and to have disabled the accounts of over 270,000 users.[3]

See also[edit]


  1. ^ Douze, Matthijs; Tolias, Giorgos; Pizzi, Ed; Papakipos, Zoë; Chanussot, Lowik; Radenovic, Filip; Jenicek, Tomas; Maximov, Maxim; Leal-Taixé, Laura; Elezi, Ismail; Chum, Ondřej; Ferrer, Cristian Canton (February 21, 2022). "The 2021 Image Similarity Dataset and Challenge". arXiv. arXiv:2106.09672. Image fingerprints, such as PhotoDNA from Microsoft, are used throughout the industry to identify images that depict child exploitation and abuse
  2. ^ a b c d "The Rise of Content Cartels". February 11, 2020. Retrieved August 21, 2022.
  3. ^ a b Hill, Kashmir (August 21, 2022). "A Dad Took Photos of His Naked Toddler for the Doctor. Google Flagged Him as a Criminal". The New York Times. ISSN 0362-4331. Retrieved August 21, 2022.
  4. ^ a b "New Technology Fights Child Porn by Tracking Its "PhotoDNA"". Microsoft Corporation. December 15, 2009. Retrieved September 9, 2016.
  5. ^ "Photo DNA: Step by step". Microsoft. Archived from the original on September 21, 2013. Retrieved February 11, 2014.
  6. ^ "How PhotoDNA for Video is being used to fight online child exploitation". September 12, 2018.
  7. ^ a b "How PhotoDNA for Video is being used to fight online child exploitation". September 12, 2018.
  8. ^ Jackson, William (August 27, 2014). "Improved image analysis tools speed exploited children cases". GCN.
  9. ^ a b Clark, Liat (April 30, 2014). "Child abuse-tracking tech donated to the world". Wired UK.
  10. ^ 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
  11. ^ Ward, Mark (March 23, 2014). "Cloud-based archive tool to help catch child abusers". BBC News.
  12. ^ "PhotoDNA Cloud Service". Microsoft Corporation. Retrieved February 19, 2015.
  13. ^ a b Richard Allan (June 18, 2018). "Hearing at 11:14". in "The EU's horizontal regulatory framework for illegal content removal in the DSM".
  14. ^ Thu; Szoka, Feb 10th 2022 03:30pm-Berin; Cohn, Ari (February 10, 2022). "The Top Ten Mistakes Senators Made During Today's EARN IT Markup". Techdirt. Retrieved August 21, 2022.{{cite web}}: CS1 maint: numeric names: authors list (link)
  15. ^ Schmon, Christoph (June 3, 2021). "The EU Commission's Refusal to Let Go of Filters". Electronic Frontier Foundation. Retrieved August 21, 2022.
  16. ^ "Upload filters: a danger to free internet content?". IONOS Digitalguide. March 28, 2019. Retrieved August 21, 2022.
  17. ^ "Fighting illegal online hate speech: first assessment of the new code of conduct". December 6, 2016. Retrieved August 21, 2022.
  18. ^ "The EU Code of conduct on countering illegal hate speech online | European Commission". Retrieved August 29, 2022.
  19. ^ "Code of Practice on Disinformation | Shaping Europe's digital future". September 26, 2018.
  20. ^ "The 2022 Code of Practice on Disinformation | Shaping Europe's digital future". March 24, 2023.
  21. ^ "Procedure File: 2014/2256(INI) | Legislative Observatory | European Parliament".
  22. ^ COMMUNICATION FROM THE COMMISSION TO THE EUROPEAN PARLIAMENT AND THE COUNCIL Guidance on Article 17 of Directive 2019/790 on Copyright in the Digital Single Market
  23. ^ "Terrorist content online".
  24. ^ Reuter, Markus; Rudl, Tomas; Rau, Franziska; Hildebr, Holly. "Why chat control is so dangerous". European Digital Rights (EDRi). Retrieved August 21, 2022.
  25. ^ Waddell, Kaveh (June 22, 2016). "A Tool to Delete Beheading Videos Before They Even Appear Online". The Atlantic. Retrieved September 10, 2016.
  26. ^ "Partnering to Help Curb Spread of Online Terrorist Content | Facebook Newsroom". Retrieved December 6, 2016.
  27. ^ Abelson, Hal; Anderson, Ross; Bellovin, Steven M.; Benaloh, Josh; Blaze, Matt; Callas, Jon; Diffie, Whitfield; Landau, Susan; Neumann, Peter G.; Rivest, Ronald L.; Schiller, Jeffrey I.; Schneier, Bruce; Teague, Vanessa; Troncoso, Carmela (October 14, 2021). "Bugs in our Pockets: The Risks of Client-Side Scanning". arXiv:2110.07450 [cs.CR].
  28. ^ Hill, Kashmir (August 21, 2022). "A Dad Took Photos of His Naked Toddler for the Doctor. Google Flagged Him as a Criminal". The New York Times. ISSN 0362-4331. Retrieved August 21, 2022. A bigger breakthrough came along almost a decade later, in 2018, when Google developed an artificially intelligent tool that could recognize never-before-seen exploitative images of children. [...] When Mark's and Cassio's photos were automatically uploaded from their phones to Google's servers, this technology flagged them.
  29. ^ "Google Flagged Parents' Photos of Sick Children as Sexual Abuse". Gizmodo. August 22, 2022. Retrieved August 28, 2022. According to Google, those incident reports come from multiple sources, not limited to the automated PhotoDNA tool.
  30. ^ Roth, Emma (August 21, 2022). "Google AI flagged parents' accounts for potential abuse over nude photos of their sick kids". The Verge. Retrieved August 28, 2022. Google has used hash matching with Microsoft's PhotoDNA for scanning uploaded images to detect matches with known CSAM. [...] In 2018, Google announced the launch of its Content Safety API AI toolkit that can "proactively identify never-before-seen CSAM imagery so it can be reviewed and, if confirmed as CSAM, removed and reported as quickly as possible." It uses the tool for its own services and, along with a video-targeting CSAI Match hash matching solution developed by YouTube engineers, offers it for use by others as well.
  31. ^ "Unfortunate Truths about Child Pornography and the Internet [Feature]". December 7, 2012.
  32. ^ Eher, Reinhard; Craig, Leam A.; Miner, Michael H.; Pfäfflin, Friedemann (2011). International Perspectives on the Assessment and Treatment of Sexual Offenders: Theory, Practice and Research. John Wiley & Sons. p. 514. ISBN 978-1119996200.
  33. ^ Lattanzi-Licht, Marcia; Doka, Kenneth (2004). Living with Grief: Coping with Public Tragedy. Routledge. p. 317. ISBN 1135941513.
  34. ^ Arthur, Charles (July 22, 2013). "Twitter to introduce PhotoDNA system to block child abuse images". The Guardian. Retrieved July 22, 2013.
  35. ^ Smith, Catharine (May 2, 2011). "Facebook Adopts Microsoft PhotoDNA To Remove Child Pornography". Huffington Post. Retrieved July 22, 2013.
  36. ^ "Adobe & PhotoDNA". Retrieved August 27, 2021.
  37. ^ "Reddit use PhotoDNA to prevent child pornography". March 19, 2020.
  38. ^ "Discord Transparency Report: July — Dec 2020". Discord Blog. April 2, 2021. Retrieved May 8, 2022.
  39. ^ "Microsoft tip led police to arrest man over child abuse images". The Guardian. August 7, 2014.
  40. ^ Salcito, Anthony (December 17, 2009). "Microsoft donates PhotoDNA technology to make the Internet safer for kids". Retrieved July 22, 2013.

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