Yes, we have met with Continuum and other reps of companies that are
producing and selling CD-ROMs of images of art works in museums and
private collections. Museums may be selling the rights to digitized image
reproduction to companies like Continuum but most, if not all, are not
selling exclusive rights. That is, the copyright owner retains the
right to resell the image, etc. I have written this without double-checking
but believe it essentially correct. And, as most probably know, museums and
private collectors do not always own the copyright to all works in their
collections.