Many may not realise this, but because Eiffel Tower was built in 1889 it falls within the "Public Domain" Under an obscure EU rule you are permitted to take a photograph of the tower during the day. However, during the evening when the tower is lit up it is considered to be an art work and in the words of a notice at the tower itself:
".............. its various illuminations are subject to author's rights as well as brand rights. Usage of these images is subject to prior request from the 'Société d'Exploitation de la Tour Eiffel' (the Eiffel Tower's operating company, or SETE)"