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Yeah I'm curious how their hashing mechanism works. Like, is it a straight up sha hash of the image or something a little more sophisticated that wouldn't be fo

Yeah I'm curious how their hashing mechanism works. Like, is it a straight up sha hash of the image or something a little more sophisticated that wouldn't be fooled by minor edits? Though in the latter case can that even technically be considered hashing? I guess it all depends on how they're doing it which brings us back to my first question...

evgen 9y ago
It is called PhotoDNA and was developed by Microsoft. This is the same tech that is used to find child porn images even when people go to various lengths to prevent simple hashing from being able to determine photo similarity. It works surprisingly well at the task from what I have seen/heard.
- b4lancesh33t 9y ago
  Photo dna is just one of a class of algorithms called perceptual image hashes (there are also perceptual audio and video hash algorithms). They by no means invented the technique, just one particular branded implementation of it.
FRex 9y ago
Hash by strictest definition is just a function that maps any input to fixed size output. There is a special subcategory of hashes that are locality sensitive and change a little when input changes a little, just like there is a special subcategory of crypto hashes. See: https://en.wikipedia.org/wiki/Locality-sensitive_hashing https://en.wikipedia.org/wiki/Locality-sensitive_hashing Technology for searching for similar images (I have no idea how it works interally) already exists and is very widely deployed. You can easily find an image similar (uncropped, cropped, with different filter, greyed, ungreyed, with a logo in corner, etc.) to your input image on https://tineye.com/ https://tineye.com/ and https://images.google.com https://images.google.com .
15155 9y ago
They're (more than likely - almost certainly) using proprietary image fingerprinting techniques. If you had access to the original implementation, you could probably defeat them permanently with minimal alteration via reverse engineering. Which is why you don't have access to the original software, its specifications, or implementation details. (https://twitter.com/alexstamos/status/928646228472078336 https://twitter.com/alexstamos/status/928646228472078336)

evgen 9y ago

It is called PhotoDNA and was developed by Microsoft. This is the same tech that is used to find child porn images even when people go to various lengths to prevent simple hashing from being able to determine photo similarity. It works surprisingly well at the task from what I have seen/heard.

b4lancesh33t 9y ago
Photo dna is just one of a class of algorithms called perceptual image hashes (there are also perceptual audio and video hash algorithms). They by no means invented the technique, just one particular branded implementation of it.

FRex 9y ago

Hash by strictest definition is just a function that maps any input to fixed size output. There is a special subcategory of hashes that are locality sensitive and change a little when input changes a little, just like there is a special subcategory of crypto hashes. See: https://en.wikipedia.org/wiki/Locality-sensitive_hashing https://en.wikipedia.org/wiki/Locality-sensitive_hashing Technology for searching for similar images (I have no idea how it works interally) already exists and is very widely deployed. You can easily find an image similar (uncropped, cropped, with different filter, greyed, ungreyed, with a logo in corner, etc.) to your input image on https://tineye.com/ https://tineye.com/ and https://images.google.com https://images.google.com .

15155 9y ago

They're (more than likely - almost certainly) using proprietary image fingerprinting techniques. If you had access to the original implementation, you could probably defeat them permanently with minimal alteration via reverse engineering. Which is why you don't have access to the original software, its specifications, or implementation details. (https://twitter.com/alexstamos/status/928646228472078336 https://twitter.com/alexstamos/status/928646228472078336)