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"The researchers scanned for the abusive images by looking for their “hashes” — corresponding bits of code that identify them" I can't find the actual study, b

"The researchers scanned for the abusive images by looking for their “hashes” — corresponding bits of code that identify them" I can't find the actual study, but I am wondering if anyone actually verified the photos are CSAM, and not a collision or even just misidentified images? There is substantial evidence that the technique used is highly likely to produce false positives when ran on a large dataset like this.

ensignavenger 3y ago
Found the study- https://stacks.stanford.edu/file/druid:kh752sm9123/ml_training_data_csam_report-2023-12-20.pdf https://stacks.stanford.edu/file/druid:kh752sm9123/ml_traini... The study says 825 were confirmed using one method, and 183 with another- not clear to me if those are unique or duplicates of each other. Also, "confirmed" only means "is or is likely" CSAM, and they don't provide any numbers as to how many were classified as "likely". It also isn't clear how they define "likely". EDIT: Previously I said the article was overstating the number of CSAM images found, but I since re-read it and the article may be citing the correct total from the two methods)
Buttons840 3y ago
I thought quality hashing algorithms have no known collisions? Like, it's theoretically possible, it just has never happened, anywhere, not even once. Why would a collision happen here?
- ensignavenger 3y ago
  Cryptographic hashes aren't supposed to have collisions... the types of hashing that PhotoDNA and other similar systems use are not cryptographic. In fact, some say they aren't even real hashes. The reason for this is because they want images that have been altered to still match, whereas with a cryptographic has, even a minor change will change the hash. So it is more a a "similarity" check than a proper hash.
- yencabulator 3y ago
  You're confusing hashing as in SHA-256 with perceptual hashing, which is more like a blurry thumbnail of an image converted into numbers. Any minor alteration to an image will change it's cryptographic hash completely, making those pretty poor tools for finding images that might want to be hidden. Perceptual hashing should match e.g. resized versions of the image, but with them two "blurry thumbnail hashes" can match accidentally.

ensignavenger 3y ago

Found the study- https://stacks.stanford.edu/file/druid:kh752sm9123/ml_training_data_csam_report-2023-12-20.pdf https://stacks.stanford.edu/file/druid:kh752sm9123/ml_traini... The study says 825 were confirmed using one method, and 183 with another- not clear to me if those are unique or duplicates of each other. Also, "confirmed" only means "is or is likely" CSAM, and they don't provide any numbers as to how many were classified as "likely". It also isn't clear how they define "likely". EDIT: Previously I said the article was overstating the number of CSAM images found, but I since re-read it and the article may be citing the correct total from the two methods)

Buttons840 3y ago

I thought quality hashing algorithms have no known collisions? Like, it's theoretically possible, it just has never happened, anywhere, not even once. Why would a collision happen here?

ensignavenger 3y ago
Cryptographic hashes aren't supposed to have collisions... the types of hashing that PhotoDNA and other similar systems use are not cryptographic. In fact, some say they aren't even real hashes. The reason for this is because they want images that have been altered to still match, whereas with a cryptographic has, even a minor change will change the hash. So it is more a a "similarity" check than a proper hash.
yencabulator 3y ago
You're confusing hashing as in SHA-256 with perceptual hashing, which is more like a blurry thumbnail of an image converted into numbers. Any minor alteration to an image will change it's cryptographic hash completely, making those pretty poor tools for finding images that might want to be hidden. Perceptual hashing should match e.g. resized versions of the image, but with them two "blurry thumbnail hashes" can match accidentally.