In the absence of a formal identity document, a driver's license may be accepted in many countries for identity verification.

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Many countries require all foreigners to have a passport or occasionally a national identity card from their country available at any time if they do not have a residence permit in the country.

The identity document is used to connect a person to information about the person, often in a database.

The photo and the possession of it is used to connect the person with the document.

The connection between the identity document and information database is based on personal information present on the document, such as the bearer's full name, age, birth date, address, an identification number, card number, gender, citizenship and more.

A unique national identification number is the most secure way, but some countries lack such numbers or don't write them on identity documents.

but it did not become widely used until the early 20th century when photographs became part of passports and other ID documents such as driver's licenses, all of which came to be referred to as "photo IDs".

Both Australia and Great Britain, for example, introduced the requirement for a photographic passport in 1915 after the so-called Lody spy scandal.

An identity document (also called a piece of identification or ID, or colloquially as papers) is any document which may be used to prove a person's identity.

If issued in a small, standard credit card size form, it is usually called an identity card (IC or ID card).