Ensuring the lawfulness of the data processing - In case of re-use of data, carrying out the necessary additional tests and verifications

07 June 2024

If it re-uses data previously collected, the data controller is required to carry out certain additional verifications to ensure that that the processing is lawful. The CNIL helps you determine your obligations, depending on the means of collecting the data and its source.

This content is a courtesy translation of the original publication in French. In the event of any inconsistencies between the French version and this English translation, please note that the French version shall prevail.

The principle

In some cases, depending on the methods of collection and the source of the data used for the creation of the training dataset, the controller is required to carry out certain verifications to ensure that the processing of data is lawful. These verifications must be carried out in addition to the identification of the legal basis for the processing.

In practice

The provider reuses the data it originally collected for another purpose

The provider reuses a publicly accessible dataset

The provider reuses a dataset acquired from a third party (data brokers, etc.)


In addition to these prior verifications, and regardless of the method of collection used, re-users must ensure that their own processing are fully compliant.

It should be noted that this obligation also applies when they reuse datasets whose creation and dissemination do not fall within the scope of French or European law. For more information on the territorial scope of the GDPR, see the how-to sheet “What is the scope of  the AI how-to sheets”.

In particular, the re-user must ensure compliance with the requirements regarding the persons whose data is present in the dataset thus obtained. They must inform them of the processing that they wish to implement, and allow them to exercise their rights. 

Please note: a dedicated sheet on the reuse of personal data will be published later. It will complement the elements introduced in this sheet, in particular with practical case studies.