Acceptable documents for Spanish citizens
The primary documents which are used for proving identities are the identity card ("Documento Nacional de Identidad", also known as "DNI") and the passport. Since every Spanish person is obliged to own an identity card from the age of 14 on you should insist that at least one of the presented documents is an id card or a passport.
You can accept also as secondary document, the driving license. Any other presented documents (club cards, birth certificates, company badges, etc) should not be accepted since they are not official identity cards at all.
Everybody in Spain over 14 must have a National Identity Card (Documento nacional de identidad usually abbreviated to DNI) issued by the National Police. On the front side there is a colour photograph, the name and two surnames (see Spanish naming customs), the bearer's signature, an id number, the issue date and the expiration date. Depending on holder's age, the card has a validity of 5 years, 10 years or indefinite (for the elderly).
On the reverse appears the birth date and place, the gender, both parents' names (if known), and the current address. At the bottom, some of the previous information is written in special characters suitable to be read by OCR.
The ID number is an eight digit number followed by a letter. The letter is only a CRC used to verify the correctness of the number. This id number is unique, and is used by the Spanish Hacienda Pública to keep track of each citizen's income taxes and financial status.
Since 2006 a new version of the 'DNI' is being introduced. The new 'Electronic DNI' is a Smart card that allows for digital signing of documents. It conveys the same printed information as the older version, but in a plastic card with a different design.
This external site describes the Electronic DNI card.
This attachment shows the electronic DNI card.
This attachment shows the old DNI card (still valid).
Currently there are two driving license formats in Spain:
1. The new credit-card-style format. It is a single plastic-coated document, very difficult to falsify. The document can be renewed every 10 or 15 years depending on the member state. The several member states have the option to include a microchip containing information about the card holder on the card. This can prove extremely useful because police are then able to access the driving license in their own language.
This attachment shows a sample of new driving license.
2. The old pink three-fold license. Licenses issued before January 1 2005 uses this old format. It is a pink three fold card with a photo stapled with a stamped sign of the Traffic authority and other stamp over the photograph. On the stamp we can read "Ministerio del Interior - Dirección General de Tráfico". Since a license can be issued for upto 10 years, all these old licenses will be invalid from 2015.
This attachment shows a sample of the old pink three-fold driving license, valid until 2015.
Image source: Autoescuela Cordellas
A passport is a document, issued by a national government, which certifies, for the purpose of international travel, the identity and nationality of its holder. The elements of identity are name, date of birth, sex, and place of birth. Most often, nationality and citizenship are congruent. In Spain most passports issued have the format of attached images, and are very similar to passports of other countries.
This attachment shows the cover of a spanish passport.
This attachment shows the identification page of a spanish passport.
Image source: flickr and public domain.