This is the conventional way of describing the relation between the artist and the work of art.
Pablo Picasso. The auction house believes this is an original work by the artist.
Pablo Picasso. Replica. The auction house believes that the artist him/herself made this work as a replica of their own, previous original.
Attributed to Pablo Picasso. The auction house finds it likely that this is an original work, but is not prepared to guarantee this.
Studio of Pablo Picasso. The auction house believes that the work was made in the artist's studio and possibly under their supervision.
Circle of Pablo Picasso. The auction house believes that the work was made by another artist but during the lifetime of the named artist and in their manner.
Follower of Pablo Picasso. The auction house believes that the work was done in the manner of the named artist, during their lifetime or later.
In the manner of Pablo Picasso. The auction house believes that the work is done in the manner of the named artist but after their lifetime.
After Pablo Picasso. The auction house believes that the work was made by another artist, based on an original work by the named artist.