Interesting that you mention WalMart. Last year I photographed a wedding for some friends. Along with a selection of finished prints, I gave them a CD with all of the image files (I had already decided that wedding photography was not for me and was therefore not interested in repeat sales.) WalMart would not print pictures from the CD until I signed a letter of permission, saying they looked like professional images. Not only did my ego soar, I appreciated the store's respect for intellectual property rights.