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Non-Reversible and Attribute Preserving Face De-Identification
Halmstad University, School of Information Technology.ORCID iD: 0000-0001-7192-9026
2025 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

De-identification, also known as anonymization, is a broad term that refers to the process of redacting or obscuring personal data, or data that identifies an individual. In the context of video and image data de-identification, the most tangible personal information is the face. Faces are considered biometric data, thus change little compared to other aspects of an individual, such as clothing and hairstyle. Humans possess a strong innate ability to recognize faces. Computers are also adept at recognizing faces, and face recognition models are exceptionally powerful at identifying and comparing faces. Consequently, it is widely recognized as crucial to obscure the faces in video and images to ensure the integrity of de-identified data. Conventionally, this has been achieved through blurring or masking techniques. However, these methods are destructive of data characteristics and thus compromise critical attribute information such as eye gaze, pose, expression and the fact that it is a face. This is a particular problem because our society is data-driven in many ways. This information is useful for a plethora of functions such as traffic safety. One obvious such aspect is autonomous driving and driver monitoring, where necessary algorithms such as object detectors rely on deep learning to function. Due to the data hunger of deep learning, combined with society's demand for privacy and integrity through regulations such as the General Data Protection Regulation (GDPR), face de-identification, which preserves useful information, becomes significantly important.

This Thesis investigates the potential and possible limitations of de-identifying faces, while preserving the aforementioned useful attribute information. The Thesis is especially focused on the sustainability perspective of de-identification, where the perseverance of both integrity and utility of data is important. The baseline method to achieve this is through methods introduced from the face swapping and face manipulation literature, where the current research focuses on changing the face (or identity) with generative models while keeping the original attribute information as intact as possible. All while being integrated and consistent in an image and/or video. Specifically, this Thesis will demonstrate how generative target-oriented and subject-agnostic face manipulation models, which aim to anonymize facial identities by transforming original faces to resemble specific targets, can be used for realistic de-identification that preserves attributes.

While this Thesis will demonstrate and introduce novel de-identification capabilities, it also addresses and highlight potential vulnerabilities and security issues that arise from naively applying generative target-oriented de-identification models. First, since state-of-the-art face representation models are typically restricting the face representation embeddings to a hyper-sphere, maximizing the privacy may lead to trivial identity retrieval matching. Second, transferable adversarial attacks, where adversarial perturbations generated by surrogate identity encoders cause identity leakage in the victim de-identification system. Third, reconstruction attacks, where bad actor models are able to learn and extract enough information from subtle cues left by the de-identification model to consistently reconstruct the original identity.

Through this, this Thesis points out several approaches that are: 1) Controllable, meaning that the proposed models do not naively change the identity. This means that the type and magnitude of identity change is adjustable, and thus tunable to ensure anonymization. 2) Subject agnostic, meaning that the models can handle any identity or face. 3) Fast, meaning that the models are able to run efficiently. Thus having the potential of running in real-time. 4) Non-reversible, this Thesis introduces a novel diffusion-based method to make generative target-oriented models robust against reconstruction attacks. The end product consists of a hybrid generative target-oriented and diffusion de-identification pipeline that achieves state-of-the-art performance on privacy protection as measured by identity retrieval, pose retention, expression retention, gaze retention, and visual fidelity while being robust against reconstruction attacks.

Place, publisher, year, edition, pages
Halmstad: Halmstad University Press, 2025. , p. 79
Series
Halmstad University Dissertations ; 130
Keywords [en]
Anonymization, Data Privacy, Generative AI, Reconstruction Attacks, Deep Fakes, Facial Recognition, Identity Tracking, Biometrics
National Category
Signal Processing
Identifiers
URN: urn:nbn:se:hh:diva-55652ISBN: 978-91-89587-77-9 (electronic)ISBN: 978-91-89587-76-2 (print)OAI: oai:DiVA.org:hh-55652DiVA, id: diva2:1945494
Public defence
2025-04-17, S3030, Kristian IV:s väg 3, Halmstad, 10:00 (English)
Opponent
Supervisors
Available from: 2025-03-19 Created: 2025-03-18 Last updated: 2025-03-19Bibliographically approved
List of papers
1. Towards Privacy Aware Data collection in Traffic: A Proposed Method for Measuring Facial Anonymity
Open this publication in new window or tab >>Towards Privacy Aware Data collection in Traffic: A Proposed Method for Measuring Facial Anonymity
2021 (English)In: Fast-Zero 2021 Proceedings: 6th International Symposium on Future Active Safety Technology toward Zero Accidents, Chiyoda: JSAE , 2021Conference paper, Published paper (Refereed)
Abstract [en]

Developing a machine learning-based vehicular safety system that is effective and generalizes well, capable of coping with all the different scenarios in real traffic is a challenge that requires large amounts of data. Especially visual data for when you want an autonomous vehicle to make decisions based on peoples’ possible intent revealed by the facial expression and eye gaze of nearby pedestrians. The problem with collecting this kind of data is the privacy issues and conflict with current laws like General Data Protection Regulation (GDPR). To deal with this problem we can anonymise faces with current identity and face swapping techniques. To evaluate the performance and interpretation of the anonymization process, there is a need for a metric to measure how well these faces are anonymized that takes identity leakage into consideration. To our knowledge, there is currently no such investigation for this problem. However, our method is based on current facial recognition methods and how recent face swapping work determines identity transfer performance. Our suggestion is to utilize state-of-the-art identity encoders like FaceNet and ArcFace to make use of the embedding vectors to measure anonymity. We provide qualitative results that show the applicability of publicly available identity encoders for measuring anonymity. We further strengthen the applicability of how these encoders behave on the VGGFace2 dataset compared to samples that have had their identity changed by Faceshifter, along with a survey regarding the anonymization procedure to pinpoint how strong facial anonymization is compared the vector distance measurements.

Place, publisher, year, edition, pages
Chiyoda: JSAE, 2021
Keywords
data collection, facial recognition, interpretation, anonymization
National Category
Computer Sciences
Identifiers
urn:nbn:se:hh:diva-52895 (URN)
Conference
Fast Zero´21, Society of Automotive Engineers of Japan, Online, 28-30 September, 2021
Available from: 2024-03-18 Created: 2024-03-18 Last updated: 2025-03-18Bibliographically approved
2. Comparing Facial Expressions for Face Swapping Evaluation with Supervised Contrastive Representation Learning
Open this publication in new window or tab >>Comparing Facial Expressions for Face Swapping Evaluation with Supervised Contrastive Representation Learning
2021 (English)In: 16th IEEE International Conference on Automatic Face and Gesture Recognition (FG 2021): Proceedings / [ed] Vitomir Štruc; Marija Ivanovska, Piscataway: IEEE, 2021Conference paper, Published paper (Refereed)
Abstract [en]

Measuring and comparing facial expression have several practical applications. One such application is to measure the facial expression embedding, and to compare distances between those expressions embeddings in order to determine the identity- and face swapping algorithms' capabilities in preserving the facial expression information. One useful aspect is to present how well the expressions are preserved while anonymizing facial data during privacy aware data collection. We show that a weighted supervised contrastive learning is a strong approach for learning facial expression representation embeddings and dealing with the class imbalance bias. By feeding a classifier-head with the learned embeddings we reach competitive state-of-the-art results. Furthermore, we demonstrate the use case of measuring the distance between the expressions of a target face, a source face and the anonymized target face in the facial anonymization context. © 2021 IEEE.

Place, publisher, year, edition, pages
Piscataway: IEEE, 2021
National Category
Computer Sciences
Identifiers
urn:nbn:se:hh:diva-46506 (URN)10.1109/FG52635.2021.9666958 (DOI)000784811600027 ()2-s2.0-85125063047 (Scopus ID)978-1-6654-3176-7 (ISBN)
Conference
16th IEEE International Conference on Automatic Face and Gesture Recognition, FG 2021, Virtual, Jodhpur, India, 15- 18 December, 2021
Available from: 2022-04-21 Created: 2022-04-21 Last updated: 2025-03-18Bibliographically approved
3. FaceDancer: Pose- and Occlusion-Aware High Fidelity Face Swapping
Open this publication in new window or tab >>FaceDancer: Pose- and Occlusion-Aware High Fidelity Face Swapping
2023 (English)In: Proceedings - 2023 IEEE Winter Conference on Applications of Computer Vision, WACV 2023, Piscataway: IEEE, 2023, p. 3443-3452Conference paper, Published paper (Refereed)
Abstract [en]

In this work, we present a new single-stage method for subject agnostic face swapping and identity transfer, named FaceDancer. We have two major contributions: Adaptive Feature Fusion Attention (AFFA) and Interpreted Feature Similarity Regularization (IFSR). The AFFA module is embedded in the decoder and adaptively learns to fuse attribute features and features conditioned on identity information without requiring any additional facial segmentation process. In IFSR, we leverage the intermediate features in an identity encoder to preserve important attributes such as head pose, facial expression, lighting, and occlusion in the target face, while still transferring the identity of the source face with high fidelity. We conduct extensive quantitative and qualitative experiments on various datasets and show that the proposed FaceDancer outperforms other state-of-the-art networks in terms of identityn transfer, while having significantly better pose preservation than most of the previous methods. © 2023 IEEE.

Place, publisher, year, edition, pages
Piscataway: IEEE, 2023
Keywords
Algorithms, Biometrics, and algorithms (including transfer, low-shot, semi-, self-, and un-supervised learning), body pose, face, formulations, gesture, Machine learning architectures
National Category
Signal Processing
Identifiers
urn:nbn:se:hh:diva-48618 (URN)10.1109/WACV56688.2023.00345 (DOI)000971500203054 ()2-s2.0-85149000603 (Scopus ID)9781665493468 (ISBN)
Conference
23rd IEEE/CVF Winter Conference on Applications of Computer Vision, WACV 2023, Waikoloa, Hawaii, USA, 3-7 January 2023
Available from: 2022-11-15 Created: 2022-11-15 Last updated: 2025-03-18Bibliographically approved
4. FIVA: Facial Image and Video Anonymization and Anonymization Defense
Open this publication in new window or tab >>FIVA: Facial Image and Video Anonymization and Anonymization Defense
2023 (English)In: 2023 IEEE/CVF International Conference on Computer Vision Workshops (ICCVW), Los Alamitos, CA: IEEE, 2023, p. 362-371Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, we present a new approach for facial anonymization in images and videos, abbreviated as FIVA. Our proposed method is able to maintain the same face anonymization consistently over frames with our suggested identity-tracking and guarantees a strong difference from the original face. FIVA allows for 0 true positives for a false acceptance rate of 0.001. Our work considers the important security issue of reconstruction attacks and investigates adversarial noise, uniform noise, and parameter noise to disrupt reconstruction attacks. In this regard, we apply different defense and protection methods against these privacy threats to demonstrate the scalability of FIVA. On top of this, we also show that reconstruction attack models can be used for detection of deep fakes. Last but not least, we provide experimental results showing how FIVA can even enable face swapping, which is purely trained on a single target image. © 2023 IEEE.

Place, publisher, year, edition, pages
Los Alamitos, CA: IEEE, 2023
Series
IEEE International Conference on Computer Vision Workshops, E-ISSN 2473-9944
Keywords
Anonymization, Deep Fakes, Facial Recognition, Identity Tracking, Reconstruction Attacks
National Category
Computer Sciences
Identifiers
urn:nbn:se:hh:diva-52592 (URN)10.1109/ICCVW60793.2023.00043 (DOI)2-s2.0-85182917356 (Scopus ID)9798350307443 (ISBN)
Conference
2023 IEEE/CVF International Conference on Computer Vision Workshops (ICCVW 2023), Paris, France, 2-6 October, 2023
Available from: 2024-02-08 Created: 2024-02-08 Last updated: 2025-03-18Bibliographically approved
5. Adversarial Attacks and Identity Leakage in De-Identification Systems: An Empirical Study
Open this publication in new window or tab >>Adversarial Attacks and Identity Leakage in De-Identification Systems: An Empirical Study
2025 (English)In: IEEE Transactions on Biomedical Engineering, ISSN 0018-9294, E-ISSN 1558-2531, p. 1-18Article in journal (Refereed) Submitted
Abstract [en]

In this paper, we investigate the impact of adversar- ial attacks on identity encoders within a realistic de-identification framework. Our experiments show that the transferability of attacks transfers from an external surrogate model to the system model (e.g., CosFace to ArcFace), allows the adversary to cause identity information to leak in a sufficiently sensitive face recognition system. We present experimental evidence and propose strategies to mitigate this vulnerability. Specifically, we show how fine-tuning on adversarial examples helps to mitigate this effect for distortion-based attacks (i.e., snow, fog, etc.), while a simple low-pass filter can attenuate the effect of adversarial noise without affecting the de-identified images. Our mitigation results in a de-identification system that preserves its functionality while being significantly more robust to adversarial noise. 

Place, publisher, year, edition, pages
Piscataway, NJ: IEEE, 2025
Keywords
De-Identification, Adversarial Attacks, Adversarial Transferability
National Category
Computer Sciences
Identifiers
urn:nbn:se:hh:diva-55647 (URN)
Available from: 2025-03-18 Created: 2025-03-18 Last updated: 2025-03-18Bibliographically approved
6. HYDRO: Towards Non-Reversible Face De-Identification Using a High-Fidelity Hybrid Diffusion and Target-Oriented Approach
Open this publication in new window or tab >>HYDRO: Towards Non-Reversible Face De-Identification Using a High-Fidelity Hybrid Diffusion and Target-Oriented Approach
Show others...
(English)In: Article in journal (Refereed) Submitted
Abstract [en]

Target-oriented face de-identification models aim to anonymize facial identities by transforming original faces to resemble specific targets. Such models commonly lever- age generative encoder-decoder architectures to manip- ulate facial appearances, enabling them to produce re- alistic high-fidelity de-identification results, while ensur- ing considerable attribute-retention capabilities. However, target-oriented models also carry the risk of inadvertently preserving subtle identity cues, making them (potentially) reversible and susceptible to reconstruction attacks. To address this problem, we introduce a novel robust face de-identification approach, called HYDRO, that combines target-oriented models with a dedicated diffusion process specifically designed to destroy any imperceptible informa- tion that may allow learning to reverse the de-identification procedure. HYDRO first de-identifies the given face im- age, injects noise into the de-identification result to im- pede reconstruction, and then applies a diffusion-based re- covery step to improve fidelity and minimize the impact of the noising process on the data characteristics. To further improve image fidelity and better retain gaze directions, a novel Eye Similarity Discriminator (ESD) is also intro- duced and incorporated it into the training of HYDRO. Ex- tensive quantitative and qualitative experiments on three diverse datasets demonstrate that HYDRO exhibits state- of-the-art (SOTA) fidelity and attribute-retention capabili- ties, while being the only target-oriented method resilient against reconstruction attacks. In comparison to multiple SOTA competitors, HYDRO reduces the success of recon- struction attacks by 85.7% on average. The code is avail- able at: https://github.com/anonymousiccv2025/HYDRO.

National Category
Computer graphics and computer vision
Identifiers
urn:nbn:se:hh:diva-55649 (URN)
Conference
International Conference on Computer Vision, ICCV 2025, Honolulu, Hawaii, Oct 19 – 23th, 2025
Available from: 2025-03-18 Created: 2025-03-18 Last updated: 2025-03-18Bibliographically approved

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