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CGI-DM: Digital Copyright Authentication for Diffusion Models via Contrasting Gradient Inversion
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Proposes CGI-DM, a post-fine-tuning copyright authentication method that masks half of an image, recovers it by maximizing the KL divergence (via noise-prediction loss differences, Monte Carlo sampling and PGD) between pre-trained and fine-tuned diffusion models, and flags training membership by recovery similarity.
Problem
Determining whether a diffusion model was few-shot fine-tuned on a given image (unauthorized use of artworks or photos) is hard because generative outputs are diverse and rarely closely match training samples; existing post-hoc checks give only binary, non-visual evidence.
Approach
Remove part of an image and recover the missing content by gradient-based inversion that maximizes the difference in noise-prediction error between the pre-trained and fine-tuned models (a closed-form surrogate of the KL divergence between their latent trajectories); high similarity between recovered and original images indicates membership.
Key results
- On WikiArt under Dreambooth (w. prior loss), CGI-DM reaches 0.90 Acc (C) and 0.96 AUC (C) for style-driven authentication, versus at best 0.82 Acc and 0.89 AUC for the img2img baseline.
- On the Dreambooth object dataset, CGI-DM achieves 0.84 Acc (C) and 0.90 AUC (C) under Dreambooth (w. prior loss), outperforming the best baseline (0.67 Acc, 0.73 AUC).
- Accuracy stays above 0.88 across SD v1.4, v1.5, v2.0 and AltDiffusion, and remains around 0.90 across 5 to 50 training images.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| use CGI-DM instead of Img2img | copyright authentication on WikiArt · Dreambooth with prior loss | AUC (D): 0.82 -> 0.92 | Helped |
| use CGI-DM instead of Img2img | copyright authentication on Dreambooth dataset · Dreambooth with prior loss | AUC (D): 0.82 -> 0.91 | Helped |
| replace Stable Diffusion v1.4 with Stable Diffusion v1.5 (ablation) | CGI-DM · WikiArt | AUC (D): 0.98 -> 0.99 | Helped |
| replace Stable Diffusion v1.4 with Stable Diffusion v2.0 (ablation) | CGI-DM · WikiArt | AUC (D): 0.98 -> 0.98 | No clear effect |
| replace Stable Diffusion v1.4 with AltDiffusion (ablation) | CGI-DM · WikiArt | AUC (D): 0.98 -> 0.99 | Helped |
| increase training images from 10 to 20 (ablation) | CGI-DM · WikiArt | AUC (D): 0.98 -> 0.97 | Hurt |
| increase training images from 10 to 50 (ablation) | CGI-DM · WikiArt | AUC (D): 0.98 -> 0.99 | Helped |
| add horizontal-flip augmentation during training (ablation) | CGI-DM · WikiArt | AUC (D): 0.98 -> 0.98 | No clear effect |
| add Cutout during training (ablation) | CGI-DM · WikiArt | AUC (D): 0.98 -> 0.97 | Hurt |
| add RandAugment during training (ablation) | CGI-DM · WikiArt | AUC (D): 0.98 -> 0.92 | Hurt |
| use fine-grained block-wise masking instead of large half-image masking or blurring (ablation) | CGI-DM · WikiArt | copyright authentication performance | Helped |
| increase extraction steps beyond approximately 1000 (ablation) | CGI-DM · WikiArt | accuracy | No clear effect |
Surprising findings
- Directly applying gradient inversion yields little useful signal for diffusion models, which is why the contrast between pre-trained and fine-tuned models is needed.
- Masking with large contiguous regions produced recovered content unrelated to the target, so fine-grained block-wise masking was needed.
Limitations
- Accuracy drops under RandAugment defense (about 10% Acc reduction) and the method relies on the attacker's fine-tuned model being available for comparison.
- Evaluation is limited to few-shot fine-tuning on small sets (5 to 50 images) of WikiArt and Dreambooth; the paper notes its approach needs a proper threshold for the similarity metric.
Experimental setup
Datasets: WikiArt Dreambooth
Benchmarks: WikiArt Dreambooth
Metrics: Accuracy AUC CLIP similarity DINO similarity
Baselines: Text-to-image generation pipeline Image-to-image generation pipeline DDNM inpainting pipeline
Builds on: DDIM Anti-DreamBooth Dreambooth PGD adversarial attack Model inversion attacks
Closest papers by meaning
- Harnessing Frequency Spectrum Insights for Image Copyright Protection Against Diffusion Models (CVPR 2025 · similarity 0.89)
- Disguised Copyright Infringement of Latent Diffusion Models (ICML 2024 · similarity 0.88)
- The Stronger the Diffusion Model, the Easier the Backdoor: Data Poisoning to Induce Copyright BreachesWithout Adjusting Finetuning Pipeline (ICML 2024 · similarity 0.87)
- Leveraging Model Guidance to Extract Training Data from Personalized Diffusion Models (ICML 2025 · similarity 0.87)
- Watermark-embedded Adversarial Examples for Copyright Protection against Diffusion Models (CVPR 2024 · similarity 0.87)
- CDI: Copyrighted Data Identification in Diffusion Models (CVPR 2025 · similarity 0.87)
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