En garde!

What a funny to-do!  Go to Paris during the day, and you can take as many pictures of the Eiffel Tower from as many angles as you like.  But go back at night and you are not allowed to photograph it.  Why not?  Well the Tower itself is what is known as "in the public domain" and therefore fair game for anyone who wants to take its picture. But at night it is lit up, and this illumination constitutes an artistic work which cannot be reproduced (e.g. by photographing it) without the permission of the artist.  Of course this is theory - it is unlikely that you will be hauled off to be en taule just for taking a personal snap, but you have been warned!