It was previously considered to be in the public domain because it is a scan (or similar) by the Bibliotheque Nationale de France, but not everything scanned by the BNF is automatically in the public domain.
It is possible that this file is in the public domain for other reasons, for example because it was published a long time ago (anything before ca. 1900 is most likely ok) or because its author / artist / photographer died over 70 years ago and it was published over 95 years ago. In such cases, a new rationale should be applied, and a different license tag (see Commons:Licensing and valid license tags at Commons:Copyright tags) should be used.
If the file is not found to be in the public domain, it might be nominated for deletion (NOT by any automatic process, but manually).
See below for the previous rationale (not applicable anymore).
Previous public domain rationale, no longer applicable
Public domain works must be out of copyright in both the country of origin and the United States, and must be accompanied one or more valid copyright tags to indicate its status. Absence of such tags may result in a file's deletion.
Public domain works must be out of copyright in both the United States and in the source country of the work in order to be hosted on the Commons. If the work is not a U.S. work, the file must have an additional copyright tag indicating the copyright status in the source country. Note: This tag should not be used for sound recordings.PD-1923Public domain in the United States//commons.wikimedia.org/wiki/File:Btv1b53206412n_Port_militaire_de_Brest.jpg
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