artist-interface-with-rect is a variable defined in `artist.el'.
Its value is

Whether to interface with the rect package or not.

Interfacing to the rect package means that the Copy and Paste operations
will use the rectangle buffer when accessing the copied area. This means
that you can insert a rectangle which is copied using the artist package
and vice versa.

If this causes any problem for you (for example, if the implementation of
the rectangle package changes), you can set this variable to nil, and the
artist package will use its own copy buffer.

You can customize this variable.