Some countries like the UK have a "Sweat of the Brow" [0] doctrine which lets them claim copyright by virtue of the effort put in to compile the work. However it isn't recognized in the U.S because they doesn't see this as requiring creativity so it doesn't count as a derivative work. This has the benefit that companies can't circumvent the public domain without altering the work, but it also disincentives them from digitizing older works. I don't know if french law acknowledges the doctrine or not. Regardless it is pretty unbecoming of a project started by government archivists and headed by a national library, though I do understand that they might want to recoup some of their costs.
But the site with the reproductions is hosted[1] in the USA[2], right? If so, then one could conclude that there is no copyright on the digital reproductions.
I think the copyright notice at the bottom is just website boilerplate. it's also on the main Stanford library website. The about page says "For commercial use, contact: utilisation.commerciale@bnf.fr", so it is the Bibliothèque nationale de France that is claiming copyright. IANAL, but I think you'd be pretty safe using those images on servers hosted in the USA because then you'd be under the jurisdiction of U.S copyright law, but things can get messy as in this case where a British Museum threatened to take the Wikimedia Foundation to UK court: https://en.wikipedia.org/wiki/National_Portrait_Gallery_and_....
The original image might be out of copyright, but someone's photograph of it is not.
So, if you can take your own image you can do what you want with it, but you don't have any right to someone else's photograph of it.
