A licensing agreement is written permission the artist gives to a client for a specific use for a specified length of time of any creative work for a predetermined price. Just because companies are paying for your art doesn’t necessarily mean that they own it. Because of the nature of the development of storyboards, clients almost always own all rights (see later). Artists have historically sold all rights for preproduction work.
When I am working as an independent contractor, I state upfront, and confirm on my invoice, that the fees I charge are for preproduction purposes only. I give clients one copy of my invoice, and I have them sign and return a second copy for my records.