An important decision for the illustrator is to decide whether they are assigning their work or licensing it. This is an important consideration when drafting or signing a contract.
Generally this means that the illustrator is handing over all ownership rights of the artwork. The purchaser has total control over the art produced, to reproduce it as many times as they like or make changes as they please. Once the illustrator has completed the assignment, he or she has no claim to how the artwork is handled.
If the agreement is entered to sell “all substantial rights” then the payment is generally made as a single advance payment (or in installments, due upon completion of the assignment).
Unless specified, an illustrator retains the legal ownership of his or her artwork. Although someone else may publish or reproduce the artwork, the terms are generally limited by licensing guidelines.