They don't say anything about how to determine the value. In general, it seems to me that this decision will create a lot of uncertainty about what is copyright

They don't say anything about how to determine the value. In general, it seems to me that this decision will create a lot of uncertainty about what is copyrighted and what is free. They do say that the test is whether someone _could_ sell it for money, so the fact that in this case Wikimedia is a non-profit and does it for free does not affect the outcome.