As a person that works in a photolab, I can promise you that most walmart type quick labs often ignore any copyright marks on the image, once customers, grown adults, start screaming at the 17 year old employees, they just print off some crummy prints for them to make them go away. And thats IF the lab clerk even checks or cares.

There is no solution other then to show them the quality available when its left in your hands, and maybe contrasting that to something done from a quick lab from a crummy scan.