Elements 13 photo of print with white background

The photos (one shown) are of prints of sailing vessels with no background detail - just white. (Don't worry - we own the copyright of the prints which we sell on the web, but the photos there show too much distortion). The new photos we have taken are not perfect and show some greying in the white.  Even using RAW we cannot figure out how to whiten ALL the background without affecting other colors. Since there are many prints there is white background in far too many places between the rigging and sails and text to use the magic wand. I need to whiten all the background (including between sails and rigging and text) to ffffff without affecting any other colors of the vessel, sails, flags etc. Any ideas?