I licensed mine as a commercial use licence giving the artist the ability to use the image on products indefinitely. It also stated that no editing rights had been granted. The licence also stated that once the images were accepted that all future edits would be at my hourly rate. I also always put in a little caveat that if any terms are broken all licences are void and all usage rights return to me. This discourages some of the horrendous InstaSnapFace filters being applied to one of my images. For your use case it would be more appropriate to licence in a manner that vintagesnaps has described. Agree that my licence was for a different use but the principal is the same.