[roywiggins]

Not quite trivial: people can crop, skew, vignette, mirror, timestretch and scale video to try to defeat it. YouTube's Content ID seems to be vulnerable to this sort of thing still.

[x0x0]

I think that's why many of these systems focus on audio. It's harder to change in a way that beats fingerprinting but doesn't ruin the viewing experience.

[izelpii]

I think the majority of the cases are uploaders that basically post the same content.