Privacy-preserving image-matching lets platforms automatically catch known abuse material — quietly powering most of the tips that rescue kids.
The situation, the move, the outcome.
In 2009, Microsoft and Dartmouth built PhotoDNA and donated it to the National Center for Missing & Exploited Children. It converts an image into a numerical fingerprint, or hash, and matches it against a database of known child sexual abuse material — without a human 'looking at' anyone's photos. Used by Google, Facebook, Reddit, Discord and many others, it has helped detect and remove millions of images, convict offenders, and in some cases rescue victims. One investigator estimated about 90% of her cases now originate from PhotoDNA-powered CyberTipline reports.
Why it matters beyond one family.
PhotoDNA shows that safety and privacy aren't opposites: hashing catches known illegal content automatically while keeping ordinary users' images private. It's invisible infrastructure doing enormous good.
How to apply it.
- Understand that major platforms already scan for known abuse material.
- Report suspected abuse imagery to NCMEC rather than handling it yourself.
- Favor platforms that participate in hashing and safety programs.
Concrete next steps.
- Report to NCMEC's CyberTipline (CyberTipline.org) or the IWF (UK).
- Use Take It Down / StopNCII for a young person's own images.
- Keep evidence and involve the FBI where there's coercion.
Read it for yourself.
- Microsoft — PhotoDNA microsoft.com ↗
- Thorn — PhotoDNA leads the fight against abuse imagery thorn.org ↗
- Wikipedia — PhotoDNA en.wikipedia.org ↗
Call or text 988 (Suicide & Crisis Lifeline, 24/7) · Text HOME to 741741 (Crisis Text Line) · Find a child psychiatrist at aacap.org · For immediate danger, call 911.