It's called Photo ID number. It's generally a personal information such Passport or Driving License and shouldn't usually be published.
The regulations differ on almost every country and generally no one can do anything by using your ID number.
More info is provided on
Wikipedia and it's free. Why don't you just read that?
People searching for others' IDs are intending to create fake accounts on variety of companies such PayPal(tm) and they need a picture of the Photo ID. So, a picture does not mean a number.
The PayPal(tm) European regulations automatically close accounts having a negative balance and directly contact the account's holder to take the money back. If the Photo ID is yours then you will have to pay that.
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