3 ms·

>>Why not just send the hash? Is there an app for that? /s To be honest, this is a great idea. I think its something that should be built into OS's -- selec

• amelius 9y ago
  On the other hand, malevolent people could modify the image until its hash changes (e.g. by cropping, changing colors, etc.)
• Matt3o12_ 9y ago
  This should be really difficult for images because different devices saves them different. The iPhone 7 and new use the HEIC format, however they are uploaded as jpeg to my iPad and Mac because they don’t support the new format (no hardware optimization). Now chances are, when I share it on my iPhone, it regenerates the jpeg again, but a bit differently, yet unnoticable by humans. This makes it impossible to use a conventional hashing algorithm for images because an undetectable change for images because an invisible change can change the hash and even alomost every byte and yet it looks completely the same. Of course, every user can do that knowingling, just crop the image a very tiny bit or change one color of one pixel and the hash is going to be completely different.
  • Corrado 9y ago
    You could possibly use a perceptual hash[0] to compare images. While building an image processing application I used the pHashion library to compare thumbnails to their originals to make sure it still looked "the same" to humans. It worked very well and might be useful in the case of comparing "nude" photos to a reference. [0] http://phash.org/ http://phash.org/ [1] https://github.com/westonplatter/phashion https://github.com/westonplatter/phashion