License Project Description

I have a question: I’d like to use an item for a project. Basically, I’ve been asked to do a graphic work from a client that will sell the end product to a third person. In this case, if I add to my graphic an item downloaded from here, what should I write in in the project’s name? Should I register it specifying my client’s name or the third person (that I don’t have anything to do with)?

Thanks a lot!