Franck, I would love to see a photo, but I know very little about copyright laws, so I cannot say. I suspect that copyright laws in various countries would prohibit such a posting.
On the other hand, I cannot see why you cannot explain in your own words what the necklace looks like. I don't think that would break any copyright laws, and it would help us enormously.
If you do that could you clearly describe which necklace you are describing = for example the Cartier 1901 Cartier Indian necklace or one of the possible 2 colliers resille necklaces.