> I think the host should be held accountable if they keep allowing the same harmful content to be uploaded again and again. The first occurrence is their notice. Future occurrences is negligence.
On this, I fully support your view. Something as trivial as a keeping list of hashes, to prevent repeat uploads of the exact same binary content, is incredibly easy to implement and I would fault any major hoster for not doing it. But people quickly learn to re-encode or subtly alter the content, so hashes, size, number of frames, etc don't match.
Perceptual hashes are a lot more expensive computationally, should be much harder to dodge, but even youtube, which supposedly has the best minds behind it, copes very poorly with the many popular evasion techniques (slight distortion, horizontal mirroring, superimposing a couple thin lines, showing the content in the left pane, while showing nonsense in the right pane, etc etc) so I'm not sure they're a viable option.
Can you really hold the hoster at fault when the technology doesn't exist, or is impractically slow and expensive? Would you rather have no hosters?