You may only record data you genuinely need for a clearly defined and lawful purpose. The fact that information is visible on the identity card does not mean you may record all of it.
What is usually needed
For ordinary personnel administration you may need, among other things, surname, first names, date of birth, necessary contact or address details and, where legally permitted or required, the national identification number (in Belgium the rijksregisternummer or INSZ number). Nationality or residence status may be relevant when you have to check whether someone has the right to work in your country.
For foreign workers, the type and validity period of a residence or work permit may also be relevant.
What you do not record by default
Do not record the photograph, signature, card number, place of issue or expiry date by default. The national identification number is specifically protected, and the photograph, signature and card number increase the risk of identity fraud.
The Belgian data protection authority confirms that only data strictly necessary for the stated purpose may be read, and highlights the special conditions that apply to the photograph and the national register number. You can read more about the latter in Can I use and keep an employee’s national identification number?
How to approach it
Collect the data directly from the employee where possible, for example through an onboarding form, and use the card only to check visually that it is correct.
Maintain an onboarding data list that states the purpose and legal basis for each field, and assign every employee a separate internal employee number. Keeping a copy of the card is a separate question: Can I keep a copy of an employee’s identity card?
Legal basis
The selection of data follows from the principles of purpose limitation and data minimisation (Article 5(1)(b) and (c) GDPR). Every record requires a legal basis under Article 6 GDPR, and under Article 13 GDPR the employee must know which data you keep and why. Article 87 GDPR lets member states set specific conditions for the use of the national identification number. Which data you actually have to record is determined by national legislation on social documents, social security declarations, identity cards and population registers.
GDPRWise maps your HR processes, from onboarding to offboarding, so you know for every data item why you keep it.