Digital creations are often carried out jointly by many creators. It is then necessary to provide protection to the creatorship of each participating creator. This paper proposes a novel digital watermarking framework to solve the problem of joint-creatorship protection. The proposed framework makes use of digital watermarking techniques and cryptographic protocols to achieve the creatorship protection purpose in jointly created digital images. The framework embeds multiple watermarks in a spatially non-overlapping manner during the creation process and thus obtains a high visual quality for the watermarked digital image. The complexity of the framework is analyzed by calculating the data transmission and storage requirements, and the experimental results show that the framework can address the joint-creatorship protection problem with low storage and transmission requirements.