Comment by heavyset_go

I agree, and maybe I'm wrong, but I see a similarity between phash quantization and DCT and ML kernels. I think you could craft "invisible" adversarial images similarly for phash systems like you can ML ones and the results could be just as bad. They'd probably replicate better than adversarial ML images, too.

I think the premise for either system is flawed and both are too error prone for critical applications.