Hacker News Reader

> The whole idea of a perceptual hash is that the more similar the two hashes are, the more similar the two images are

If that is the case, then the word "hash" is terribly mis-applied here.

Hash is applied correctly here. A hash function is "any function that can be used to map data of arbitrary size to fixed-size values." The properties of being a(n) (essentially) unique fingerprint, or of small changes in input causing large changes in output, are properties of cryptographic hashes. Perceptual hashes do not have those properties.

Good explanation, thanks. I only knew about cryptographic hashes, or those that are used for hash tables where you absolutely do not want to have collisions. Anyhow, I'm not really comfortable with this usage of the word "hash". It is completely opposite of the meaning I'm used to.

Maybe the term fingerprint is better

Reply on news.ycombinator.com