As long as item is not claimed by anyone and the owner is unknown, you can be the administrator of the item (note: not the owner!). In accordance to the Dutch legislation of lost and found, you are obliged to store the found item for a period of 3 months when the value of the item is less than EUR 450. When the value of the item is more than EUR 450 you have to store it for a period of 12 months. If, after this mandatory storage period, the owner is still unknown, you may keep the found item or decide what will happen with this item.
Would you like to know everything about the Dutch legislation of lost and found? [Please read the following page](https://ilost.co/wetgeving-gevonden-voorwerpen). Unfortunately, this page is only in Dutch.
As laws and legislations vary from country to country, please check your local laws and legislations on lost and found items.