Re: how exactly were the school to know of the copyright in the first place?
All images are copyright and you must obtain permission to use them. If you don't know who owns the copyright then you still can't use it. NB. differences in law here in some situations in some countries, eg. the "safe harbour" clause of the US DMCA which provides a workaround for sites like YouTube. Andrew Orlowski has argued that this effectively encourages abuse of copyright by Google, et al. But that doesn't apply here.
Biting the hand that feeds IT
