What is image hashing used for?

Question

I hear this term sometimes and am wondering what it is used for?

Answer 1

hashing in general is a useful way to reduce a huge amount of data to a short(ish) number that can be used to identify that image.

They are sometimes intended just to provide a handy way to identify a file without the intervention of a human, especially in the presence of several parallel authors who can't be relied upon to increment some master counter (JPG001 JPG002) without overlapping.

Sometimes hashes are intended to be unforgeable, so that I can say - if the image hash YOU generate is the same as the one I made when I sent you the image, then you can be sure it's from me (and not adjusted by an evildoer). However, not all hashes can make this guarantee, an every few years a popular such 'cryptographic' hash is shown to have fatal flaws.