Nicolas VIGNERON, 03/01/2018 17:34:
So now, I'm sending you this mail to know whether you had to deal with things like this or if you have any ideas of what should be done.
Assuming the copyfraudster has already been kindly pointed to https://commons.wikimedia.org/wiki/COM:REUSE, the next step is for the photographer to take action. He can try with the friendly http://photoclaim.com/en/.
Given the strong moral rights laws in France, lex loci protectionis and various previous court rulings, I'd expect the lawyers to threaten a lawsuit for a few thousands euro and quickly settle for less.
I also usually go fetch suggestions from https://wiki.creativecommons.org/wiki/Case_Law but I don't see anything from France there.
Federico