We spent a morning at a special exhibition of Andy Warhol's work at the Grand Palais.
No photos are ever allowed in special exhibitions almost anywhere in the world, due to private lender's restrictions and copyright laws.
This sign outside the entrance says it all, with Warhol's quintessential image of Ethel Scull, wife of Robert Scull, an early collector of Pop Art.

In 1963, New York taxi cab business owner Robert Scull commissioned Warhol to make a large image of his wife similar to the one Warhol had done of Marilyn Monroe.
Warhol had pictures of Ethel Scull made in an automatic ID-photo machine, creating 300 passport size photos of her,.
He then made an enormous multi-face portrait of her using 36 of the images.
This billboard advertising the Warhol exhibit is a portion of that large format image.