What is the difference between a graphic work “by” Picasso versus “after” Picasso?
The convention in the art world is that the phrase “by” Picasso (or “by” any other artist) means the artist worked directly on the original plate. For a lithograph, this means the artist drew on the original plate or on the original transfer paper. For an etching, this means the artist inscribed or etched the image on the original copper plate.
The phrase “after” Picasso (or “after” any other artist) means that a skilled artisan created the image on the original plate based on some original work that was by created the artist. For example, Picasso created many oil paintings throughout his career. Some of these were reproduced later as lithographs on paper. These “after” works were approved by Picasso, but a skilled artisan created the original lithographic plate rather than Picasso himself.
There is no automatic correlation of “by” and “after” to “hand signed” and “hand numbered”. Some works “by” Picasso are hand signed and hand numbered, but some are not. Some works “after” Picasso are hand signed and hand numbered, but again some are not.
One more meaning of “after” … if one artist is familiar with a work by another artist, then creates their own version of the same image or theme, but in their own distinctive style, that new work can be said to be “after” the original artist.