A method to control a display of at least one content on a screen connected to a processing platform, said content comprising access conditions, said method comprising: - acquiring an image of a sensitive area, the sensitive area being an area in which content displayed on the screen is within the field of view of an observer placed thereat, - detecting on the image a number of potential observers within the sensitive area, the number of detected observers being at least two, - requesting or trying to obtain credentials from each of the detected observers within the sensitive area, and acquiring a number of credentials from the detected observers within the sensitive area, the acquisition of the credentials comprising: - receiving, via a wireless communication device, an identifier of the respective detected observer stored in a data carrier carried by said detected observer, and retrieving the credential of said detected observer using the received identifier, and/or - receiving, via the wireless communication device, the credentials of the respective detected observer stored in the data carrier carried by said detected observer; - comparing the number of credentials acquired with the number of detected observers, and depending on the outcome of the comparing: - if the number of credentials is below the number of detected observers, disabling the display of the content, - if the number of credentials is equal to the number of detected observers, comparing each credential with the access conditions and if all credentials match the access conditions, enabling display of the content; wherein the method further comprises: - the processing platform constantly or repeatedly requesting acquisition of a further image of the sensitive area, and determining whether the number of detected observers has changed; - when the number of detected observers decreases, the processing platform continuing to allow the display of the content, and - when the number of detected observers increases to a number previously detected, the processing platform comparing a previous image from before the number of observers decreased in order to determine whether a same face has reappeared and: - if true, continuing to enable the display of the content; - if false, disabling the display of the content and requesting credentials of a newly detected observer. - acquiring an image of a sensitive area, the sensitive area being an area in which content displayed on the screen is within the field of view of an observer placed thereat, - detecting on the image a number of potential observers within the sensitive area, the number of detected observers being at least two, - requesting or trying to obtain credentials from each of the detected observers within the sensitive area, and acquiring a number of credentials from the detected observers within the sensitive area, the acquisition of the credentials comprising: - receiving, via a wireless communication device, an identifier of the respective detected observer stored in a data carrier carried by said detected observer, and retrieving the credential of said detected observer using the received identifier, and/or - receiving, via the wireless communication device, the credentials of the respective detected observer stored in the data carrier carried by said detected observer; - receiving, via a wireless communication device, an identifier of the respective detected observer stored in a data carrier carried by said detected observer, and retrieving the credential of said detected observer using the received identifier, and/or - receiving, via the wireless communication device, the credentials of the respective detected observer stored in the data carrier carried by said detected observer; - comparing the number of credentials acquired with the number of detected observers, and depending on the outcome of the comparing: - if the number of credentials is below the number of detected observers, disabling the display of the content, - if the number of credentials is equal to the number of detected observers, comparing each credential with the access conditions and if all credentials match the access conditions, enabling display of the content; - if the number of credentials is below the number of detected observers, disabling the display of the content, - if the number of credentials is equal to the number of detected observers, comparing each credential with the access conditions and if all credentials match the access conditions, enabling display of the content; - the processing platform constantly or repeatedly requesting acquisition of a further image of the sensitive area, and determining whether the number of detected observers has changed; - when the number of detected observers decreases, the processing platform continuing to allow the display of the content, and - when the number of detected observers increases to a number previously detected, the processing platform comparing a previous image from before the number of observers decreased in order to determine whether a same face has reappeared and: - if true, continuing to enable the display of the content; - if false, disabling the display of the content and requesting credentials of a newly detected observer. - if true, continuing to enable the display of the content; - if false, disabling the display of the content and requesting credentials of a newly detected observer.