  Web-based AI image generation has become an innovative art form that can
generate novel artworks with the rapid development of the diffusion model.
However, this new technique brings potential copyright infringement risks as it
may incorporate the existing artworks without the owners' consent. Copyright
infringement quantification is the primary and challenging step towards
AI-generated image copyright traceability. Previous work only focused on data
attribution from the training data perspective, which is unsuitable for tracing
and quantifying copyright infringement in practice because of the following
reasons: (1) the training datasets are not always available in public; (2) the
model provider is the responsible party, not the image. Motivated by this, in
this paper, we propose CopyScope, a new framework to quantify the infringement
of AI-generated images from the model level. We first rigorously identify
pivotal components within the AI image generation pipeline. Then, we propose to
take advantage of Fr\'echet Inception Distance (FID) to effectively capture the
image similarity that fits human perception naturally. We further propose the
FID-based Shapley algorithm to evaluate the infringement contribution among
models. Extensive experiments demonstrate that our work not only reveals the
intricacies of infringement quantification but also effectively depicts the
infringing models quantitatively, thus promoting accountability in AI
image-generation tasks.
