Originally Posted by
Brobbel
In the Netherlands it is prohibited to make a copy for identifcation, except for government, financial institutes and employers.
Inside the Dutch passport is written:
“Dit paspoort is eigendom van de staat der Nederlanden. De houder is verplicht het paspoort zorgvuldig te bewaren. Het mag slechts ter beschikking van een derde worden gesteld, indien daartoe een wettelijke verplichting bestaat.”
"This passport is the property of the State of the Netherlands. The holder must carefully keep the passport. It may only be made available to a third set, if there is a legal obligation. "
So it is (except when ordered by the government) illegal to let them keep your passport.
It may be illegal under Dutch law, but Dutch law doesn't apply when you are out of the country.