[heavyset_go]

> And now they will evolve by developing a simple system to modify pixels in images when they copy and transmit that will easily defeat this hashing system

They don't use simple file hashes to match images, but perceptual hashes. That way they can find modified derivatives of a source image. The problem with this approach, though, is that this is ripe for false positives. Two completely unrelated images can have similar hashes.

[sterlind]

could you use multiple perceptual hash functions with different salts, so that collisions would be less likely while allowing derivatives to be detected?

[tatersolid]

That reduces to just inventing a “fancier” single hash function. This adds no value or security in cryptography; it just makes things slower. I expect the same is true of perceptual hashes.

[heavyset_go]

They aren't just matching exact hash hits, but are using a metric like the hamming distance between hashes to determine if one image is the same as , or a derivative of, another. The data structures that allow for efficient lookups rely on that metric, or another metric, for matching.