The case law and doctrine are broadly in agreement that when a person is seen in public, for example in a public place, they are giving their tacit consent. This consent is deduced from the concrete circumstances. Similarly, in principle no authorisation is required to take and use images of a crowd.
However, if you are the main subject of the photo, even if its main objective is to "show" the activities and atmosphere of the festival, you have the right to oppose:
* the taking of the photograph and/or
* its dissemination.
You can state your opposition directly to the photographer on the day of the event or subsequently by sending an email to firstname.lastname@example.org.
As a reminder, for children under the age of 14, parental consent is required for the taking and dissemination of photographs.
Further information on this subject: https://www.autoriteprotectiondonnees.be/droit-image