"Repost this image is a violation of copyright law"

So it says
What it doesn't say is no artist will ever bother bringing you to court considering just how expensive it is, also if you're in a country that doesn't apply the same copyright laws as in the US/EU, it may not apply at all; Not even to mention the fair use argument under the US constitution if you add commentary to it would make the warning void.

TL;DR
These warnings are just to scare random people off but doesn't really mean anything

Yes, lawyer is expensive