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). Some countries issue formal identity documents, while others may require identity verification using informal documents. When the identity document incorporates a person's photograph, it may be called photo ID. In the absence of a formal identity document, a driver's license may be accepted in many countries for identity verification. Some countries do not accept driver's licenses for identification, often because in those countries they do not expire as documents and can be old or easily forged. Most countries accept passports as a form of identification.Some countries require all people to have an identity document available at any time. 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.

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